ARC Insights and Resources

Dehydration of methyl lactate to acrylic acid and methyl acrylate was experimentally evaluated over a Na-FAU zeolite catalyst impregnated with multifunctional diamines. 1,2-Bis(4-pyridyl)ethane (12BPE) and 4,4′-trimethylenedipyridine (44TMDP), at a nominal loading of 40 wt % or two molecules per Na-FAU supercage, afforded a dehydration selectivity of 96 ± 3% over 2000 min time on stream. Although 12BPE and 44TMDP have van der Waals diameters approximately 90% of the Na-FAU window opening diameter, both flexible diamines interact with internal active sites of Na-FAU as characterized by infrared spectroscopy. During continuous reaction at 300 °C, the amine loadings in Na-FAU remained constant for 12BPE but decreased as much as 83% for 44TMDP. Tuning the weighted hourly space velocity (WHSV) from 0.9 to 0.2 h^–1 afforded a yield as high as 92% at a selectivity of 96% with 44TMDP impregnated Na-FAU, resulting in the highest yield reported to date.

The effect of UV irradiation on titanium dioxide catalyzed glucose conversion in value added molecules was studied at high temperatures, 120–150 °C, in anaerobic conditions. The reaction was implemented in a batch reactor designed to combine high temperature/pressure and irradiation. Inhibition of the titanium dioxide catalytic performances to produce gluconic acid was observed upon UV irradiation which allows the selective formation of levulinic acid in high yield, ~ 60% at 150 °C, together with the co-production of ethylene and hydrogen in the gas phase. The formation of levulinic acid could be explained by the creation of Brønsted acidity in the reaction medium upon irradiation. The reasons of this phenomenon are discussed considering that UV could modify the electronic properties of titanium dioxide by electron-holes pairs formation and the possible H⁺ promotion.

Solid base metal oxide catalysts such as MgO offer utility in a wide variety of syntheses from pharmaceuticals to fuels. The (111) facet of MgO shows enhanced, unique properties relative to the other facets. Carbon coatings have emerged as a promising modification to impart metal oxide catalyst stability. Here, we report the synthesis, characterization, and catalytic properties of commercial MgO, MgO(111), and carbon coated derivatives thereof for 2-pentanone condensation. The dimer and trimer products of this reaction can be used as precursors for biofuels upon oxygen removal and thus have relevance in environmental sustainability. MgO(111) maintained impressive selectivity towards the dimer product after carbon coating, whereas the other catalysts experienced a decrease in conversion and selectivity as a consequence of the carbon coating. Our findings highlight the catalytic efficacy of MgO(111), provide insight into carbon coating for catalyst stability, and pave the way for continued mechanistic investigations.

Precise control of electron density at catalyst active sites enables regulation of surface chemistry for optimal rate and selectivity to products. Here, an ultrathin catalytic film of amorphous  alumina (4 nm) was integrated into a catalytic condenser device that enabled tunable electron depletion from the alumina active layer and correspondingly stronger Lewis acidity. The catalytic condenser had the following structure: amorphous alumina/graphene/HfO2 dielectric (70 nm)/p-type Si. Application of positive voltages up to +3 V between graphene and the p-type Si resulted in electrons flowing out of the alumina; positive charge accumulated in the catalyst. Temperature programmed surface reaction of thermocatalytic isopropanol dehydration to propene on the charged alumina surface revealed a shift in the propene formation peak temperature of up to ΔTpeak~50 ⁰C relative to the uncharged film, consistent with a 16 kJ mol-1 (0.17 eV)  reduction in the apparent activation energy. Electrical characterization of the thin amorphous alumina film by ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling microscopy (STM) indicates the film is a defective semiconductor with an appreciable density of in-gap electronic states. Density functional theory calculations of isopropanol binding on the pentacoordinate aluminum active sites indicate significant binding energy changes (ΔBE) up to 60 kJ mol-1 (0.62 eV) for 0.125 e- depletion per active site, supporting the experimental findings. Overall, the results indicate that  continuous and fast electronic control of thermocatalysis can be achieved with the catalytic condenser device.

Passivation of naturally occurring AAEM in biomass enhances sugar yields from the fast pyrolysis of biomass by preventing these metals from catalyzing the fragmentation of pyranose rings in cellulose and hemicellulose. However, because AAEM also catalyzes lignin depolymerization, its passivation can be accompanied by undesirable char agglomeration. Pretreatment of biomass with ferrous sulfate both passivates AAEM and substitutes ferrous ions as lignin depolymerization catalysts. This pretreatment has been particularly successful for high ash biomass like corn stover, but of limited value for low ash biomass like wood. This study explores the reasons for this discrepancy and offers a combined pretreatment of ferrous sulfate and ferrous acetate pretreatment to overcome char agglomeration in wood. This new pretreatment increased sugar yields from 4.4 wt% to 15.5 wt% and 5.4 wt% to 19.0 wt% for hardwood and softwood biomasses, respectively. This pretreatment produces an iron-rich biochar that catalyzes oxidation of the biochar under the oxygen-rich conditions of autothermal pyrolysis, which is preferentially consumed to provide the enthalpy for pyrolysis, preserving bio-oil as a more desirable energy product. Instead of producing carbon monoxide, which dominates oxidation of biochar from untreated biomass, the iron catalyzes oxidation to carbon dioxide, producing more energy per mole of oxygen consumed. In fact, oxygen demand to support autothermal pyrolysis of red oak and southern yellow pine was reduced 15% by the presence of iron in the biochar.

Oxidative coupling of methane (OCM) presents a direct route to upgrade methane to higher value hydrocarbons in the presence of an oxidant. There have been extensive efforts dedicated to studying the initial coupling reactions to form ethylene, but there has been much less emphasis on further molecular weight growth to C₃⁺ species since it was first noted in the 1990′s. Here, catalysts were first screened for OCM activity and production of C₃⁺ during operation at high methane conversion, especially within the more-recently developed family of A₂WO₄-MnO_x/SiO₂ (A=none, Li, Na, K, Rb, Cs) catalysts. Within these, K and Rb presented a similar OCM performance to that of the more popular Na-system. Ag- and La- co-doping were also assessed to follow up on recent reports of high performance, but the latter had minimal impact on C₂⁺ formation under these conditions. Ethylene and propylene concentrations rose in proportion, independent of catalyst composition, suggesting that C₃⁺ formation was a gas-phase, radical process, not occurring directly on the catalyst surface. As such, ethylene-methane co-feeds were investigated over a range of reactor conditions for Na₂WO₄-MnO_x/SiO₂, which was relatively stable over multiple days at high conversion and the most active under conventional OCM conditions. Ethylene co-feeds increased the C₃⁺ selectivity over a range of reactor conditions, but it also promoted CO_x formation. Nonetheless, this work shows that further growth of C₃⁺ species under OCM conditions can be achieved, which may be desirable under certain scenarios.

Reaction rates of catalytic cycles over supported metal catalysts are normalized by the exposed metal atoms on the catalyst surface, reported as site time yields which provide a rigorous standard to compare distinct metal surfaces. Defined as the fraction of exposed metal surface atoms to the total number of metal atoms, it is important to measure the dispersion of supported metal catalysts to report standardized rates for kinetic investigations. Multiple characterization techniques such as electron microscopy, spectroscopy and chemisorption are exploited for catalyst dispersion measurements. While effective, electron microscopy and spectroscopy are not readily accessible due to cost and maintenance requirements. Commercial instruments therefore typically rely on chemisorption measurements, but can be cost prohibitive nonetheless, hindering the ability of catalysis research to report rigorous measures of activity. Thus, a dispersion measurement technique based on gas chromatograph (GC) ubiquitous in catalysis research is proposed, based on the principle of dynamic carbon monoxide (CO) chemisorption, where number of exposed metal surface atoms are estimated based on the amount of adsorbed CO. In this technique, the supported metal catalyst is packed into a liner, and inserted in the temperature-controlled inlet of the GC. The catalyst is pre-treated, purged with inert gas, and pulses of known amount of CO are passed through it via an automated sequence. The CO chemically adsorbs on the supported metal catalyst and the unadsorbed CO is detected by the flame ionization detector/methanizer on the GC. The amount of CO adsorbed is estimated by the difference between the amount of CO pulsed and detected, translated to estimate the number of exposed metal surface atoms using a stoichiometry factor. Dispersion measurements for several group VIII metal catalysts were conducted using this technique to demonstrate its applicability across a range of weight loadings and support identities. An agreement between catalyst dispersion measured using this technique and commercially available instruments indicated the reliability of this technique. The amount of dispersed metal as low as 0.02 mg could be estimated by this technique.

Photocatalytic conversion of CO₂ to generate high-value and renewable chemical fuels and feedstock presents a sustainable and renewable alternative to fossil fuels and petrochemicals. Currently, there is a dearth of kinetic understanding to inform better catalyst design, especially at uniform reaction conditions across diverse catalytic species. In this work, we investigate 12 active, stable, and unique but common nanoparticle photocatalysts for CO₂ reduction at room temperature and low partial pressure in aqueous phase: TiO₂, SnO₂, and SiC deposited with silver, gold, and platinum. Our analysis reveals a single consistent chemical kinetic mechanism, which accurately describes the yield and selectivity of all single-carbon containing (C1) products obtained in spite of the diverse catalysts employed. Formaldehyde is predicted as the first product in the reaction network and we report, to the best of our knowledge, the highest selectivity to date toward formaldehyde during CO₂ photoreduction when compared against all other C1 products (∼80%) albeit at low CO₂ conversion (<0.5 μmol g_cat^–1 h^–1, <16.8 nmol m^–2 h^–1). Further, we observe a volcano-like relationship between the electron-transfer rate of a given photocatalyst for CO₂ reduction and the net rate at which reduced products are produced in the reaction mixture taking into account unfavorable product oxidation. We establish an empirical upper limit for the maximum rate of production of CO₂ reduction products for any nanoparticle photocatalyst in the absence of a hole-scavenging agent. These results form the basis for the design and optimization of the next generation of highly efficiency and active photocatalysts for CO₂ reduction.

In Chapter I, we proposed to study a model system of polyurethane consisting of polyol and CO2 instead of a complete polyurethane formulation. By studying a simple system, we could focus on a single driving force for the nucleation of bubbles—the supersaturation of dissolved CO2—which simplified instrument development (Chapter III) and analysis of nucleation (Chapter VI). However, bubble nucleation in polyurethane is affected by the many other components involved, such as chemically reactive isocyanate, hydrocarbon-based physical blowing agents (PBAs), water (chemical blowing agent), surfactants, catalysts, and flame retardant, and the processing conditions, such as temperature increase and cross-linking reaction. While a high-quality polyurethane foam typically requires each of these aspects to work in concert, studying the effect of adding each one-by-one on bubble nucleation can elucidate the specific role of each in a way that previous work on complete formulations cannot.

In 2018 13.7 EJ of fuel were consumed by the global commercial aviation industry. Worldwide, demand will increase into the foreseeable future. Developing Sustainable Aviation Fuels (SAFs), with decreased CO₂ and soot emissions, will be pivotal to the on-going mitigation efforts against global warming. Minimizing aromatics in aviation fuel is desirable because of the high propensity of aromatics to produce soot during combustion. Because aromatics cause o-rings to swell, they are important for maintaining engine seals, and must be present in at least 8 vol% under ASTM-D7566. Recently, cycloalkanes have been shown to exhibit some o-ring swelling behavior, possibly making them an attractive substitute to decrease the aromatic content of aviation fuel. Cycloalkanes must meet specifications for a number of other physical properties to be compatible with jet fuel, and these properties can vary greatly with the cycloalkane chemical structure, making their selection difficult. Building a database of structure-property relationships (SPR) for cycloalkanes greatly facilitates their furthered inclusion into aviation fuels. The work presented in this paper develops SPRs by building a data set that includes physical properties important to the aviation industry. The physical properties considered are energy density, specific energy, melting point, density, flashpoint, the Hansen solubility parameter, and the yield sooting index (YSI). Further, our data set includes cycloalkanes drawn from the following structural groups: fused cycloalkanes, n-alkylcycloalkanes, branched cycloalkanes, multiple substituted cycloalkanes, and cycloalkanes with different ring sizes. In addition, a select number of cycloalkanes are blended into Jet-A fuel (POSF-10325) at 10 and 30 wt%. Comparison of neat and blended physical properties are presented. One major finding is that ring expanded systems, those with more than six carbons, have excellent potential for inclusion in SAFs. Our data also indicate that polysubstituted cycloalkanes have higher YSI values.

An important field of research is the miniaturization of analytical systems for laboratory applications and on-field analysis. In particular, gas chromatography (GC) has benefited from the recent advances in enabling technologies like photolithography, micromachining, hot embossing, and 3D-printing to improve sampling and sample preparation, microcolumn technologies, and detection. In this article, the developments and applications reported since 2015 were reviewed and summarized. Important applications using benchtop instruments, portable GCs, and micro-GCs (µGCs) were showcased to illustrate the current challenges associated with each miniaturized interfaces and systems. For instance, portable instruments need to be energy-efficient and ideally depend on renewable sources for carrier gas generation. Lastly, multidimensional separations were addressed using miniaturized systems to effectively improve the peak capacity of portable systems.

Ketonization of wet waste-derived carboxylic acids (volatile fatty acids, VFAs) constitutes the first step of a process to catalytically upgrade VFAs to an alkane sustainable aviation fuel blendstock. VFA ketonization has been demonstrated at near-theoretical yields at the lab scale, and robust operation of industrial-scale ketonization reactors is essential for the commercialization of VFA upgrading to sustainable aviation fuel. We present a ketonization kinetic study of hexanoic acid, a VFA model compound, over commercial ZrO₂ and use the kinetic parameters derived from the study in an adiabatic packed-bed reactor simulation of hexanoic acid ketonization running to near-complete (98%) conversion. A key findings from the kinetic study is that ketonization rate is positive order in acid pressure at low (<10 kPa) pressures and transitions to zero order at higher pressures, conforming to a Langmuir–Hinshelwood surface coupling mechanism. Rates are inhibited by ketonization coproduct water but not by ketones themselves or coproduct CO₂. Reactor simulations using these kinetics show that rate inhibition by water controls reactor size and that size requirements can be lessened by employing designs that allow for the removal of water from the partially converted acid stream.

As fumigants face increasing regulatory restrictions, resistance, and consumer pushback, it is vital to expand the integrated pest management (IPM) chemical toolkit for stored products. The production of biomass derived insecticides (e.g., bio-oil fraction) from byproducts of biofuel production may be a promising alternative source of chemistries for controlling stored product insects. These potential insecticidal bio-oils were fractionated based on boiling points (ranging from 115 to 230°C in one series and 245–250°C in another). Fractions were analyzed using GC-MS, and were found to be unique in composition. The lethality of these fractions was tested on Tribolium castaneum, Tribolium confusum, and Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). Fractions were tested at concentrations ranging from 5–260 mg/ml to screen for efficacy against adults for durations of 2–8 hr sprayed on concrete arenas. In addition, a separate assay evaluated adult emergence of larvae after 6 wk with supplemental food in arenas, while repellency was evaluated against four stored product insect species in a laminar wind tunnel. A greenhouse gas (GHG) emissions life cycle assessment was also performed, which found the use of the bio-oil fraction could reduce GHG emissions associated with the insecticide supply chain by 25–61% relative to a fossil-fuel based insecticide or pyrethroid. While adults were largely unaffected, we found that larval emergence was significantly suppressed compared to controls by roughly half or more. We also determined that there was minimal repellency to most fractions by most species. We conclude that the use of bio-oil fractions is a climate-friendly choice that may support IPM programs.

Esters represent an important class of reagents and intermediates for the production of fine chemicals and polymers. In prior studies of homogeneous catalysis, molecular complexes have been reported to selectively cleave either carbonyl C=O or acyl C-O bonds of ester to ether or alcohols, respectively. In contrast, reactions of esters and H₂ upon heterogeneous catalysts typically cleave acyl C-O bonds and produce alcohols. Here, we demonstrate that the proximity of Brønsted acid sites to Pd nanoparticles and the thermodynamic strength of these Brønsted acid sites influence the rates and selectivities toward C-O bond cleavage pathways either to ethers or alcohols during reactions of esters over bifunctional solid catalysts. The combined results from rate measurements as functions of H₂ pressure, ester conversion, and methods to combine Pd nanoparticles and acidic supports; kinetic isotope effects; in situ Brønsted acid site titrations; and calorimetric assessments of Brønsted acid strength provide evidence for bifunctional pathways that require proximity between Brønsted acid sites and Pd atoms to form ethers. These findings suggest that Brønsted acid sites near Pd nanoparticles and with lower deprotonation energies promote the direct reduction of esters to ethers by cleaving the carbonyl C=O bond. Taken together, these data indicate that direct reduction of esters to ethers involves the hydrogenation of the ester reactant to form hemiacetal at Pd nanoparticles, followed by dehydration of the hemiacetal at proximal acid sites, and subsequent hydrogenation of the enol ether. In comparison, hydrogenolysis of acyl C-O bonds of the ester reactant involves the reaction of a hydrogenated intermediate (plausibly hemiacetal) upon Pd nanoparticles to form the corresponding alcohol and aldehyde products. Among the materials examined, Pd nanoparticles supported on WO₃ catalyze the direct reduction of esters and lactones to corresponding ethers and remain stable over extended periods of time on stream (∼ 42 h). These findings offer a foundation for further design and improvement of heterogeneous catalysts for the selective reduction of esters and other challenging hydrogenations.

Thermochemical recycling of plastic waste to base chemicals via pyrolysis followed by a minimal amount of upgrading and steam cracking is expected to be the dominant chemical recycling technology in the coming decade. However, there are substantial safety and operational risks when using plastic waste pyrolysis oils instead of conventional fossil-based feedstocks. This is due to the fact that plastic waste pyrolysis oils contain a vast amount of contaminants which are the main drivers for corrosion, fouling and downstream catalyst poisoning in industrial steam cracking plants. Contaminants are therefore crucial to evaluate the steam cracking feasibility of these alternative feedstocks.

Indeed, current plastic waste pyrolysis oils exceed typical feedstock specifications for numerous known contaminants, e.g. nitrogen (∼1650 vs. 100 ppm max.), oxygen (∼1250 vs. 100 ppm max.), chlorine (∼1460 vs. 3 ppm max.), iron (∼33 vs. 0.001 ppm max.), sodium (∼0.8 vs. 0.125 ppm max.) and calcium (∼17 vs. 0.5 ppm max.). Pyrolysis oils produced from post-consumer plastic waste can only meet the current specifications set for industrial steam cracker feedstocks if they are upgraded, with hydrogen based technologies being the most effective, in combination with an effective pre-treatment of the plastic waste such as dehalogenation.

Moreover, steam crackers are reliant on a stable and predictable feedstock quality and quantity representing a challenge with plastic waste being largely influenced by consumer behavior, seasonal changes and local sorting efficiencies. Nevertheless, with standardization of sorting plants this is expected to become less problematic in the coming decade.

With appropriate pretreament, sugars can be a major product from fast pyrolysis of lignocellulosic biomass. Analytical pyrolysis of pure cellulose can produce up to 60 wt% yield of levoglucosan although yields are significantly lower in continuouos pyrolysis at larger scales. Secondary reactions of vaporized levoglucosan are thought to be responsible for this loss of sugar yield, suggesting changes in the design and operation of pyrolysis reactors to minimize these reactions. Micropyrolysis experiments were performed to better understand the mechanism of sugar degradation in the presence of biochar. A 57% loss in levoglucosan yield was observed for cellulose overlain with untreated biochar powder compared to the pure cellulose control sample. The addition of biochar derived from pyrolysis of untreated corn stover to a fluidized bed pyrolyzer reduced sugar yields from cellulose from 61.3 wt% to 21.3 wt% and 41.5–11.6 wt% for conventional and autothermal operation, respectively. The significant drop in sugar yield due to biochar interaction inspired change in feeder configuration for the fluidized bed pyrolyzer to reduce vapor-char interactions. Biomass feeding was changed from in-bed to above-bed injection, which allowed signficant devolatilization to occur above the layer of biochar that exists at the surface of the bed. By reducing secondary reactions, bio-oil and sugar yields increased by 7.9% and 14%, respectively, for autothermal pyrolysis.

Structure elucidation and quantitation of leachable impurities in pharmaceutical and medical products are crucial because unidentified and potentially toxic leachable impurities can pose health hazards to patients. Therefore, extractables and leachables (E&L) investigations have received significantly increased emphasis from regulatory agencies in recent years. Owing to the diverse chemical structures and properties of E&L compounds, various analytical challenges are encountered during their identification and quantification process. This review provides an overview of analytical challenges encountered during E&L analysis by LC-MS and GC-MS from an industrial standpoint along with the most recent advances in this field. Some of these challenges including Analytical Evaluation Threshold (AET), sample preparation, complex identification processes, and quantitation are discussed. Furthermore, the recent regulations have made analysis of E&L compounds more stringent in terms of lower AET, higher level of identification confidence and method validation requirements, necessitating the use of advanced analytical instrumentation and novel analytical approaches.

With the increasing demand for net-zero sustainable aviation fuels (SAF), new conversion technologies are needed to process waste feedstocks and meet carbon reduction and cost targets. Wet waste is a low-cost, prevalent feedstock with the energy potential to displace over 20% of US jet fuel consumption; however, its complexity and high moisture typically relegates its use to methane production from anaerobic digestion. To overcome this, methanogenesis can be arrested during fermentation to instead produce C2 to C8 volatile fatty acids (VFA) for catalytic upgrading to SAF. Here, we evaluate the catalytic conversion of food waste–derived VFAs to produce n-paraffin SAF for near-term use as a 10 vol% blend for ASTM “Fast Track” qualification and produce a highly branched, isoparaffin VFA-SAF to increase the renewable blend limit. VFA ketonization models assessed the carbon chain length distributions suitable for each VFA-SAF conversion pathway, and food waste–derived VFA ketonization was demonstrated for >100 h of time on stream at approximately theoretical yield. Fuel property blending models and experimental testing determined normal paraffin VFA-SAF meets 10 vol% fuel specifications for “Fast Track.” Synergistic blending with isoparaffin VFA-SAF increased the blend limit to 70 vol% by addressing flashpoint and viscosity constraints, with sooting 34% lower than fossil jet. Techno-economic analysis evaluated the major catalytic process cost-drivers, determining the minimum fuel selling price as a function of VFA production costs. Life cycle analysis determined that if food waste is diverted from landfills to avoid methane emissions, VFA-SAF could enable up to 165% reduction in greenhouse gas emissions relative to fossil jet.

A hydrothermal pre-treatment has been developed to improve sewage sludge quality or to produce low nitrogen biocrude via hydrothermal liquefaction (HTL) in a subsequent step. The mild hydrothermal pre-treatment (150 °C) step was performed with deionized water, sulfuric acid (0.5 M), or citric acid (0.5 M) to solubilize nitrogen containing compounds in the aqueous supernatant. Downstream, the residual solid material was liquefied with the addition of sodium carbonate via hydrothermal liquefaction (350 °C). The pre-treatment with citric acid transferred up to 66.7 wt. % of nitrogen into the aqueous supernatant, while 62.0 wt. % of carbon was recovered in the solid. Due to the pre-treatment lipids retained in the sewage sludge solid, which increased the favored biocrude yield up to 42.9 wt. % and the quality evaluating value H/Ceff ratio significantly to 1.48. Multi-method characterization of the resulted biocrude samples showed a lower concentration of N-heterocycles, while long-chain aliphatics and free fatty acid are increased.

Formaldehyde (HCHO), formed in situ by transfer dehydrogenation of methanol in methanol-to-hydrocarbon (MTH) conversion, reacts with other organic species including olefins, dienes, and aromatics to cause deactivation. The propensity of these formaldehyde-mediated pathways to cause deactivation during MTH catalysis is evaluated using site-loss selectivity and yield as numerical assessors of catalyst deactivation. The site-loss selectivity of HCHO with 0.2 kPa HCHO and 12 kPa CH3OH at 673 K decreases by 80% when co-feeding 1 kPa propylene, increases by 2× when co-feeding toluene, and increases by 150× when co-feeding 1,3-butadiene, suggesting that olefins react with HCHO in nondeactivating pathways, while aromatics and dienes react with HCHO in pathways that lead to deactivation. Further, dienes have a much higher propensity than aromatics to cause deactivation via HCHO-mediated reactions when compared on a molar basis, suggesting that dienes may be critical intermediates in HCHO-mediated deactivation pathways. This is corroborated by evidence that the site-loss selectivity of HCHO increases with increasing HCHO co-feed pressure, implying that prevalent deactivation pathways are higher order in HCHO than predominant competing nondeactivation pathways. Plausibly this occurs because HCHO reacts with itself or with a HCHO-derived species en route to deactivation, such as a diene or an aromatic, which are known products of HCHO-mediated pathways during MTH catalysis. Therefore, dienes along with HCHO should be considered as critical intermediates in fomenting deactivation in MTH catalysis and strategies to eliminate polyunsaturated species and/or intercept reaction sequences of these intermediates with HCHO will likely enhance catalyst lifetime during MTH catalysis.

The overall goal of this research was to study the effects of temperature and pine-to-HDPE ratios on the pyrolysis products. Catalytic co-pyrolysis of pine and HDPE was carried out in a double-column staged reactor, wherein the temperature was varied as 450 °C, 500 °C, and 550 °C for each pine/HDPE ratio of 0/100, 25/75, 50/50, 75/25, and 100/0. Thermal cracking of the feedstock is initiated at the first column, and the zeolitic-based ZSM-5 catalyst offered secondary cracking at a catalyst-to-feedstock ratio of 1:1 in the second column of the reactor. Catalytic pyrolysis of HDPE produced 31 wt% pyrolysis oil (40 MJ/kg calorific value) with a selectivity of above 90% toward gasoline-range hydrocarbons at 500 °C. Comparatively, pine offered 26.3% wt.% pyrolysis liquid yield with 7.9% dark pyrolysis oil (30 MJ/kg calorific value) that has a gasoline selectivity of 69.3%. Thus, the addition of HDPE increased the gasoline selectivity by increasing the hydrogen/carbon effective (H/Ceff) ratio. At pine/HDPE ratio of 25/75, the pyrolysis oil content was 22.5% at 500 °C, which is 3 times more than that of pine pyrolysis. The optimum yield and higher gasoline selectivity were observed at 500 °C for 0/100 and 25/75 pine to HDPE ratios.

Plastic buildup and accumulation in the environment are an increasingly large problem facing civilization. Petroleum-based plastics can exist for hundreds to thousands of years in the environment, destroying habitats and polluting water. Environmentally conscious replacements for plastics are urgently needed. In this publication, we present a biobased alternative to petroleum-based polycarbonates. Using a diol monomer derived from glycerol and glycerol products, we have synthesized aliphatic polycarbonates with comparable physical properties to petroleum-based incumbents. The polymer can be quantitatively depolymerized using warm methanol to recover the monomer which can be repolymerized multiple times, or alternatively, the monomer, which is inherently nontoxic, can slowly break apart to the original components. This provides two end-of-life options for this material recycle or decomposition under environmental conditions to benign building blocks, thus providing a potential pathway to avoid environmental and bioaccumulation of plastics. We also demonstrate the ability to selectively recover the monomer from a simulated mixed-plastic waste environment; the monomer recovered this way functions identically to the virgin monomer after purification. This work represents an important step in the progress toward environmentally conscious polymer design with multiple end-of-life options.

A kinetic investigation of the vapor phase Hofmann elimination of tert-butylamine over H-ZSM-5 reveals a carbocation mediated E1-like mechanism, where isobutene and ammonia are exclusively produced over Brønsted acid sites. Hofmann elimination kinetics are found to be insensitive to Al content or siting, varying only with alkylamine carbocation stability (r_tertiary > r_secondary > r_primary). Under conditions of complete tert-butylamine surface coverage, experimentally measurable apparent kinetics are directly equivalent to the intrinsic kinetics of the rate determining unimolecular surface elimination. The direct measurement of elementary step kinetics served as a water-free reactive probe, providing a direct measurement of the impact of water on solid Brønsted acid catalyzed chemistries at a microscopic level. Over a range of temperatures (453‒513 K) and tert-butylamine partial pressures (6.8×10^-2‒6.8 kPa), water reversibly inhibits the rate of Hofmann elimination. Despite expected changes in aluminosilicate hydrophobicity, the water-induced inhibition is found to be insensitive to Al content, demonstrated to be due to one water molecule per Brønsted acid site. Regardless of the significant reduction in the rate of Hofmann elimination, kinetic interrogations and operando spectroscopic measurements reveal that the coverage of TBA adsorbed on H-ZSM-5 is unaltered in the presence of water. Cooperative adsorption between the tert-butylammonium surface reactant and water adsorbed on a neighboring framework oxygen is proposed to be responsible for the observed rate inhibition, the surface dynamics of which is quantitatively captured through kinetic modeling of experimental rate measurements.

Automation of experiments is a key component on the path of digitalisation in catalysis and related sciences. Here we present the lessons learned and caveats avoided during the automation of our contactless conductivity measurement set-up, capable of operando measurement of catalytic samples. We briefly discuss the motivation behind the work, the technical groundwork required, and the philosophy guiding our design. The main body of this work is dedicated to the detailing of the implementation of the automation, data structures, as well as the modular data processing pipeline. The open-source toolset developed as part of this work allows us to carry out unattended and reproducible experiments, as well as post-process data according to current best practice. This process is illustrated by implementing two routine sample protocols, one of which was included in the Handbook of Catalysis, providing several case studies showing the benefits of such automation, including increased throughput and higher data quality. The datasets included as part of this work contain catalytic and operando conductivity data, and are self-consistent, annotated with metadata, and are available on a public repository in a machine-readable form. We hope the datasets as well as the tools and workflows developed as part of this work will be an useful guide on the path towards automation and digital catalysis.

Catalytic oxidation is a promising approach to eliminating formaldehyde (HCHO) to improve indoor air quality. Herein, CeO2 was explored due to its remarkable properties for oxygen storage and oxygen transfer capability for co-doping δ-MnO2 alongside cobalt for enhanced low-temperature oxidation of HCHO. Various characterization techniques were deployed to understand the morphology and physicochemical properties of the synthesized catalysts. The Co-Ce co-doped catalysts with low CeO2 loading (0.05 and 0.1) showed higher catalytic activity for HCHO oxidation due to their higher concentration of surface-active oxygen species. Catalytic oxidation results showed that the presence of CeO2 leads to the generation of methanol as a secondary hazardous pollutant. Methanol selectivity increases with increasing CeO2 loading in the catalysts. The results from in-situ DRIFTS confirmed the formation of methoxy species in the presence of CeO2, which are intermediates for methanol generation. Considering the recent interest in CeO2 as a potential catalyst for practical abatement of HCHO from the indoor environment, this work has thus raised questions on the safety of using CeO2 as a catalytic material for HCHO oxidation. It also provides insights into the surface reaction mechanism leading to the generation of methanol in the presence of CeO2.

We present a combined in silico and experimental study on the extraction of furfural and 5-hydroxymethylfurfural (HMF) in aqueous–organic biphasic systems. We predict the liquid–liquid equilibria and furfural/HMF partition coefficients of over 2200 water-organic biphasic systems using the multiscale COSMO-RS model and measure experimentally single-component (furfural) and mixture (furfural and HMF) partition coefficients at room and dehydration reaction-relevant temperatures in 28 solvents. We find the experimental data to be within a factor of 2 from the COSMO-RS predictions. Even though furfural and HMF have chemical similarity, the slight differences in molecular structure render the separation of furfural easier by the supply of more solvents of higher partition coefficient for extraction. We leverage this molecular difference and experimentally demonstrate that with an additional extraction step, using dichloromethane or toluene, we can selectively extract furfural from furfural-HMF mixtures, which can coexist in lignocellulosic biomass dehydration products, despite their partition coefficients being generally correlated. We complement solvent selection criteria for biphasic lignocellulosic biomass processes with a simple mass balance extraction model for determining volume ratios in multistage extraction. Finally, the molecular nature of the preferential furfural extraction is rationalized using COSMO-RS σ-profile analysis.

Through the pretreatment of lignocellulose, sugars can be major products of fast pyrolysis, most prominently the anhydrosugar levoglucosan. The analytical pyrolysis of pure cellulose can produce up to 60 wt.% yields of levoglucosan. However, in continuous pyrolysis trials, levoglucosan yields are significantly lower, suggesting that significant secondary reactions occur before the levoglucosan can be removed from the reactor and quenched. Previous research has revealed that biochar can catalyze the decomposition of levoglucosan at pyrolysis temperatures. Biochar has been shown to accumulate near the surface of a fluidized bed pyrolyzer, reaching a steady-state loading through which pyrolysis vapors must pass. However, it has not been determined whether gas-solid reactions of levoglucosan and biochar occur to an appreciable extent in a continuous fluidized bed pyrolyzer. We have performed experiments to test this hypothesis that limiting the gas-solid reactions would improve our overall bio-oil yield.
Micropyrolysis experiments were performed to better understand the mechanism of sugar degradation. A significant loss in sugar yield was observed for cellulose overlain with biochar powder compared to the pure cellulose control sample. Further tests were performed in a micropyrolyzer to investigate the effect of iron sulfate pretreated biomass which is meant to passivate the biochar’s catalytic activity. In the worst case of both biochar mixed into the sample and overlain, there was a reduction of levoglucosan from 60% to 25% with untreated biochar. On the other hand, iron sulfate biochar only saw a drop down to 53% levoglucosan yield.
Due to this drop to 25% levoglucosan in micropyrolyzer testing, the interaction between cellulose and biochar was tested using a mixture of 85 wt.% cellulose and 15 wt.% untreated corn stover biochar by continuously feeding in a fluidized bed reactor under both conventional and autothermal operation. Bio-oil produced in the reaction was recovered, and the yield of levoglucosan was determined through acid hydrolysis and HPLC analysis. Sugars decreased from 61.3 wt.% to 21.3 wt.% and 41.5 wt.% to 11.6 wt.% for conventional and autothermal operation, respectively.
The significant drop in sugar yield due to biochar interaction encouraged changes in the design or operation of continuous pyrolysis reactors to reduce vapor-product interactions with the goal of diminishing secondary reactions responsible for loss of levoglucosan yield. The injection of biomass was changed to be above the bed rather than feeding directly into the bed. This change reduced the exposure of pyrolysis vapors to the biochar layer at the fluidized bed’s surface, increasing bio-oil and sugar yields by 9.3% and 9.1%, respectively.

The oxidation kinetics for products of fast pyrolysis at low temperatures (<600 °C) are not well-known. These will be important in an effort to model autothermal pyrolysis, which has been recently developed to intensify the process but which occurs at much lower temperatures than combustion. This study determines global oxidation rates at 400–600 °C for three important products of fast pyrolysis: levoglucosan, xylose, and acetic acid. Experiments were performed in a fluidized bed pyrolyzer with the reactor modeled as a series of continuously stirred reactors and plug flow reactors to determine reaction rates. Oxidation rates at 500 °C for the three model compounds varied by a factor of 10.

Catalytic routes for upgrading CO2 to CO and hydrocarbons have been studied for decades, and yet the mechanistic details and structure–function relationships that control catalytic performance have remained unresolved. This study elucidates the elementary steps that mediate these reactions and examines them within the context of the established mechanism for CO hydrogenation to resolve the persistent discrepancies and to demonstrate inextricable links between CO2 and CO hydrogenation on dispersed Ru nanoparticles (6–12 nm mean diameter, 573 K). The formation of CH4 from both CO2–H2 and CO–H2 reactants requires the cleavage of strong C≡O bonds in chemisorbed CO, formed as an intermediate in both reactions, via hydrogen-assisted activation pathways. The C═O bonds in CO2 are cleaved via direct interactions with exposed Ru atoms in elementary steps that are shown to be facile by fast isotopic scrambling of C16O2–C18O2–H2 mixtures. Such CO2 activation steps form bound CO molecules and O atoms; the latter are removed via H-addition steps to form H2O. The kinetic hurdles in forming CH4 from CO2 do not reflect the inertness of C═O bonds in CO2 but instead reflect the intermediate formation of CO molecules, which contain stronger C≡O bonds than CO2 and are present at near-saturation coverages during CO2 and CO hydrogenation catalysis. The conclusions presented herein are informed by a combination of spectroscopic, isotopic, and kinetic measurements coupled with the use of analysis methods that account for strong rate inhibition by chemisorbed CO. Such methods enable the assessment of intrinsic reaction rates and are essential to accurately determine the effects of nanoparticle structure and composition on reactivity and selectivity for CO2–H2 reactions.

Validation of an Agilent 8890 gas chromatograph (GC) with a mass spectrometer (MS), a Polyarc reactor and flame ionization detector (FID) was performed, to try to achieve an accredited method for GC-MS/Polyarc-FID detection according to ISO 17025. The validation was carried out by evaluating chromatographic purity, accuracy, precision, instrumental repeatability, linearity, limit of detection (LOD), limit of quantification (LOQ), and robustness.
For evaluation of chromatographic purity, repeatability and robustness, a series of samples was prepared containing four different purities of the active ingredient 1-fluorododecane, spiked with the two impurities n-dodecane and n-pentadecane. The certified reference material (CRM) caffeine pharmaceutical secondary standard was used as an external standard. For results and determined purities, single values, the average, variance, standard deviation (SD), percentage relative SD (%RSD) and the measurement uncertainty was reported. Evaluation of accuracy, precision, linearity and LOD/LOQ were carried out by using four CRM solutions of benzo[a]pyrene, naphthalene, PCB 52 and caffeine. The difference in concentration from target was reported, as well as %RSD. Linearity was evaluated based on the correlation coefficient from graphic representations of the results.
The instrument was successfully validated for purity analysis. It fulfilled the set criteria for chromatographic purity, linearity, LOD, robustness and measurement uncertainty. There were problems regarding concentration verification of the CRM solutions, as well as the instrumental repeatability, where the criteria was not fulfilled. The repeatability problem was solved at the end of the project by the instrument vendor. Further work must be performed to achieve a complete validation that includes concentration verification.

Fast pyrolysis of biomass has great potential for the large-scale production of carbon negative fuels. There exist a number of problems with the technology that currently prevent the adoption of fast pyrolysis for the production of cellulosic sugars. The traditional solution of acid pretreatment, while effective at producing sugars, introduces a different set of problems that make scale up difficult. This research investigates a new approach to producing sugars from biomass fast pyrolysis without the problems associated with traditional pretreatments. Sulfuric acid passivation of the alkali and alkaline earth metals (AAEM) content of biomass has for years been the favored method for producing high yields of anhydrosugars from lignocellulosic biomass. The consequence of this treatment is a removal of catalyst for the deconstruction of the lignin fraction of biomass. Without a catalyst present lignin undergoes a phase change at elevated temperatures and melts. This melted lignin sticks to other material inside pyrolyzers forming large char agglomerates capable of plugging reactor systems. The replacement of sulfuric acid with ferrous sulfate to accomplish passivation of biomass ash content achieves the dual goals of, increasing sugar yields for corn stover from 0.9 wt% to 11.8 wt%, and catalyzing lignin deconstruction, enabling throughput increases of weight hourly space velocity from 1 h^-1 to 10 h^-1 under autothermal operation. Taken together these represent an increase in volumetric sugar productivity of an order of magnitude from 157 g L^-1h^-1 to 2041 g L^-1 h^-1. The AAEM content of biomass is detrimental to the production of sugars from fast pyrolysis of biomass. Traditional methods of acid pretreatment are effective at stopping the catalytic cracking of pyranose rings by AAEM however, they introduce the new problem of char agglomeration within continuous pyrolyzers. The new method of ferrous sulfate…

The rapid development of additive technologies in recent years is accompanied by their intensive introduction into various fields of science and related technologies, including analytical chemistry. The use of 3D printing in analytical instrumentation, in particular, for making prototypes of new equipment and manufacturing parts having complex internal spatial configuration, has been proved as exceptionally effective. Additional opportunities for the widespread introduction of 3D printing technologies are associated with the development of new optically transparent, current- and thermo-conductive materials, various composite materials with desired properties, as well as possibilities for printing with the simultaneous combination of several materials in one product. This review will focus on the application of 3D printing for production of new advanced analytical devices, such as compact chromatographic columns for high performance liquid chromatography, flow reactors and flow cells for detectors, devices for passive concentration of toxic compounds and various integrated devices that allow significant improvements in chemical analysis. A special attention is paid to the complexity and functionality of 3D-printed devices.

We introduce a comprehensive conceptual framework for selecting solvents for reactive extraction in biphasic organic-water systems and demonstrate it for the separation of HMF (5-hydroxylmethylfurfural), a platform chemical produced in the acid-catalyzed dehydration of hexoses. We first perform in silico screening of ∼2500 solvents, from the ADFCRS-2018 database using the ADF COSMO-RS implementation, and classification, based on the solvent partition coefficient. We then determine experimentally the partition coefficients for HMF, fructose, and products of HMF rehydration (levulinic acid (LA), and formic acid (FA)), the mutual water-organic solvent solubilities, and the separation factors in >50 select solvents spanning multiple homologous series at room temperature and a typical reaction temperature with in situ sampling. We find that COSMO-RS is excellent for screening purposes (typical error in most cases within a factor of ∼2). Increased temperatures lead to significant reduction in partitioning, and room temperature measurements are clearly inadequate for solvent selection. Upon down selecting classes of solvents based on separation performance, we perform experimental thermal stability and reaction compatibility studies of a small set of solvents at relevant reactive-extraction temperatures. We discover that many substituted phenols exhibit an order-of-magnitude increase in partitioning compared to conventional solvents due chiefly to hydrogen bond interactions and show the necessary stability but retain a significant fraction of water and LA, factors that need to be considered in technoeconomic analysis. In contrast, anilines, aldehydes, and acids are good to excellent regarding separation but incompatible with this specific reaction medium. This multifaceted framework can be extended to other biomass-derived products and processes

Defect engineering is an effective strategy to enhance the activity of catalysts for various applications. Herein, it was demonstrated that in addition to enhancing surface properties via doping, the influence of dopants on the surface–intermediate interaction is a critical parameter that impacts the catalytic activity of doped catalysts for low-temperature formaldehyde (HCHO) oxidation. The incorporation of Co into the lattice structure of δ-MnO₂ led to the generation of oxygen vacancies, which promoted the formation of surface active oxygen species, reduced activation energy, and enhanced catalytic activity for low-temperature oxidation of HCHO. On the contrary, Cu doping led to a drastic suppression of the catalytic activity of δ-MnO₂, despite its enhanced redox properties and slight increase in the surface concentration of active oxygen species, compared to pristine δ-MnO₂. Diffuse reflectance infrared Fourier transform analysis revealed that in the presence of Cu, carbonate intermediate species accumulate on the surface of the catalysts, leading to partial blockage of active sites and suppression of catalytic activity.

The advent of Comprehensive Two-dimensional Gas Chromatography (GC × GC) as a practical and accessible analytical tool had a considerable impact on analytical procedures associated to the so-called “omics” sciences. Specially when GC × GC is hyphenated to mass spectrometers or other multichannel detectors, in a single run it is possible to separate, detect and identify up to thousands of metabolites. However, the resulting data sets are exceedingly complex, and retrieving proper biochemical information from them demands powerful statistical tools to deal effectively with the massive amount of information generated by GC × GC. Nevertheless, the obtention of results valid on a chemical and biological standpoint depends on a deep understanding by the analyst of the fundamentals both of GC × GC and chemometrics. This review focuses on the basics of contemporary, fundamental chemometric tools applied to proccessing of GC × GC obtained from metabolomic, petroleomic and foodomic analyses. Here, we described the fundamentals of pattern recognition methods applied to GC × GC. Also, we explore how different detectors affect data structure and approaches for better data handling. Limitations regarding data structure and deviations from linearity are stressed for each algorithm, as well as their typical applications and expected output.

Manganese oxide catalysts with self-modulating K⁺ content and tunable concentration of lattice oxygen and Mn⁴⁺ were synthesized and investigated for HCHO oxidation. The preparation method affects the physicochemical properties and catalytic activity of the catalysts. Herein, the role of K⁺ in enhancing the lattice oxygen mobility of manganese oxide catalysts for enhanced formaldehyde (HCHO) is presented. The presence of K⁺ enhances the redox properties of Mn and promotes catalytic activity by enhancing the mobility of the lattice oxygen and sustaining the availability of surface active oxygen to sustain the reaction. Catalytic activity was observed to improve with increasing K⁺ content and the surface concentration of lattice oxygen and Mn⁴⁺. A drastic reduction in catalytic activity was observed in the acid-treated samples, with low K⁺ concentration. Characterization results indicate that the presence of K⁺ enhances activity and mobility of the lattice oxygen by the weakening the Mn-O bond in manganese oxide and promotes the redox properties of the catalyst. The absence of K⁺ impacted the mobility of the lattice oxygen and the ability of the catalyst to supplement the consumed oxygen species, resulting into reduced catalytic activity and deactivation in the room-temperature (30 °C) activity and stability test.

Atomically precise metallic clusters offer total structural information lacking in metal oxide and nanoparticle catalysts. However, their use as heterogeneous catalysts requires accessible and robust catalytic sites, yet directing clusters into ordered and porous assemblies through functional control remains elusive. Herein, we report a supramolecular strategy to induce permanent porosity within assemblies of two cerium oxide clusters through the capping ligands used. Single-crystal X-ray crystallography and density functional theory calculations revealed cluster assemblies with accessible channels, while adsorption isotherms showed permanent porosity. The clusters exhibited a bulk modulus >5 GPa in variable pressure diffraction studies. X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, and Raman spectroscopy demonstrated mixed valency (Ce³⁺/Ce⁴⁺) and oxygen vacancies in the clusters. We benchmarked catalytic activities through the photooxidation of 2-propanol.

We describe a two-step catalytic process for the selective and rapid conversion of biomass-derived acetylfurans into vinylfurans. This is accomplished by nearly quantitatively reducing acetylfurans into furyl alcohols using a copper chromite catalyst and exploiting the promoter-like properties of ethanol, the solvent. Subsequently, the furyl alcohol is dehydrated using solid-acid catalysts. Catalyst deactivation due to oligomeric species is a major issue, but the activity can be partially recovered by calcination. Optimization of reaction conditions showed that the selectivity could be increased by using nitrobenzene, a polar aprotic solvent. The high-boiling point solvent allows the formation of vinylfurans with a selectivity of up to 85%; the product can be isolated in high purity by distillation.

Multisubstituted pyrroles are commonly found in many bioactive small molecule scaffolds,yet thesynthesis of highly-substituted pyrrole cores remains challenging. Herein, we report an efficient catalytic synthesis of 2-heteroatom-substituted (9-BBN or SnR₃) pyrroles via Ti-catalyzed [2+2+1] heterocoupling of heteroatom-substituted alkynes. In particular, the 9-BBN-alkyne coupling reactions were found to be very sensitive to Lewis basic ligands in the reaction:exchange ofpyridine ligands from Ti to B inhibited catalysis, as evidenced by in situ ¹¹B NMR studies. The resulting 2-borylsubstituted pyrroles can then be used in Suzuki reactions in a 1-pot sequential fashion, resulting in pentasubstituted 2-aryl pyrroles that are inaccessible via previous [2+2+1] heterocoupling strategies. This reaction provides a complementary approach to previous [2+2+1] heterocouplings of TMS-substituted alkynes, which could be further functionalized via electrophilic aromatic substitution.

Fast pyrolysis is traditionally defined as the rapid decomposition of organic material in the absence of oxygen to produce primarily a liquid product known as bio-oil. However, the introduction of small amounts of oxygen to the process holds prospects of internally generating the energy needed for pyrolysis. The present study investigates the partial oxidation of lignin-derived compounds during pyrolysis, which generates both carbon oxides and aromatic carbonyl compounds. Analysis of lignin derived phenolic compounds was performed to determine if the composition had changed under oxidative conditions. NMR analyses indicates aromatic carbonyls increased under oxidative conditions, with a corresponding decrease in phenolic hydroxyl groups. Model phenolic compounds were pyrolyzed to help understand the role of partial oxidation during autothermal pyrolysis of lignocellulosic biomass.

Characterization of Extractables and Leachables (E&Ls) is an important aspect of product quality in important fields such as pharmaceuticals, medical devices and food contact materials. The main goal of an E&L study is identification and quantification of those species which may leach from packaging materials used to contain pharmaceuticals or which may leach directly out of a medical device or food contact material and thus may result in patient exposure. It is common practice to perform relative quantitation of extractables and leachables using surrogate standards due to the large diversity of species observed and the lack of available reference standards. A key problem in obtaining accurate E&L results arises due to response factor (RF) variation. Different compounds at the same concentration give different signal intensities and thus have different RF values. Two key aspects of study quality are affected by this problem. First, the evaluation of the number of compounds which are above the toxicologically relevant threshold (analytical evaluation threshold, (AET)) can be affected (RF Problem 1: AET Underreporting). Second, quantitative accuracy is affected which can reduce the reliability of the margin of safety (MOS) calculations which serves as the basis of the toxicological evaluation (RF Problem 2: Quantitative Error). RF databases have been the main solution proposed for solving these problems but do not reduce the underlying RF variation and lack the scope required to address quantitative error for compounds not contained in the database. In the absence of other solutions, large uncertainty factors (UF) have been applied in the AET calculations to account for RF Problem 1: AET Underreporting. These UF factors have been assigned values of 4 for GCMS and up to 10 for LCMS. Large uncertainty factors have a number of unintended negative consequences including the need for large amounts of sample concentration (>10X) prior to analysis resulting in potential compound loss or degradation and increased matrix effects. To overcome these problems, this publication demonstrates a multidetector approach using an HPLC system coupled with a Quadrupole Time of Flight Liquid Chromatography Mass Spectrometer (QTOF-LCMS), Charged Aerosol Detector (CAD) and an Ultraviolet-Visible Detector (UV) and a dual detection Gas Chromatography Mass Spectrometry (GCMS) system using a Polyarc Reactor system with Flame Ionization Detection (FID). Herein, it is demonstrated that this combination of methods (the multidetector approach) allowed detection and accurate surrogate standard quantitation of 217 unique extractables spanning a wide range of chemical properties (Mw, logP, pKa and boiling point). The combination of optimized detector selection with appropriate standard selection was verified to provide positive detection for 94% of the compounds at the AET level and a high level of quantitative accuracy (± 20% for 85% of the compounds and ±40% for 91% of the compounds) while using only a UF of 2. Unlike the RF database approach, the multidetector approach is not limited to only those compounds contained in the database but is applicable to the majority of extractables.

Recently, the photocatalytic conversion of glucose appeared as an environmentally friendly route to produce valuable molecules. However, the potential of this new route in comparison with the usual hydrothermal catalytic process remained questionable. In this paper, we compared the two routes using three commercial TiO2 as catalysts in the same reactor. The TiO2 superficial acidity and basicity were determined by calorimetry and FTIR of CO2, NH3 and pyridine adsorption. Relationships between the acid-base properties, the TiO2 glucose adsorption capacities measured in water and their photocatalytic or hydrothermal performances were proposed: while the photocatalytic performances could be linked to the catalysts’ Lewis acid sites density and their glucose adsorption capacities, the hydrothermal performances were dependent of the catalysts’ basic/acid sites balance. We highlighted that the conversion of glucose over TiO2 was as efficient with the photocatalytic process at ambient temperature as with the hydrothermal process at 120 °C. This underlines the potential of the photocatalytic route at the lab scale as regards to the milder experimental conditions involved.

The mechanism by which humans absorb therapeutic light in winter seasonal and nonseasonal depression is unknown. Bright-light-induced release and generation of blood-borne gasotransmitters such as carbon monoxide (CO) may be one mechanism. Here, 24 healthy female volunteers had peripheral blood samples drawn. Samples were collected in a dimly lit room and protected from light exposure. Samples were analyzed for CO concentrations by gas chromatography after 2 h of continuous exposure to darkness vs. bright white light. In a similar confirmatory study, 11 additional volunteers had samples analyzed for CO concentrations after 2 h of continuous exposure to gentle rocking in darkness vs. in bright white light. In the first study, light-unexposed peripheral blood had a mean CO concentration of 1.8 ± 0.4 SD ppm/g. Identically treated samples with 2 h of rocking and exposure to bright white light at illuminance 10,000 lux had a mean CO of 3.6 ± 1.2 ppm/g (p < 0.0001). Post hoc analysis of that study showed that time of day was significantly inversely associated with increase in CO concentration under bright light vs. dark (p < 0.04). In a smaller confirmatory study of 11 healthy female volunteers, after 2 h of rocking, light-unexposed peripheral blood had a mean CO of 1.4 ± 0.5 SD ppm/g. Identically treated blood samples with 2 h of exposure to bright white light at illuminance 10,000 lux had a mean CO of 2.8 ± 1.7 ppm/g (p < 0.02). In conclusion, bright-light exposure robustly increases human blood CO in vitro. This supports the putative role of CO as a physiological regulator of circadian rhythms and light’s antidepressant effects. This human evidence replicates earlier data from a preclinical in vivo model. This effect may be stronger in the morning than in the afternoon.

Economic viability of biofuels and bioproducts depends on system-level optimization including biomass production and conversion. Hydrothermal liquefaction (HTL) can convert wet biomass such as microalgae into biofuel intermediate (BFI) under elevated temperatures and pressure. Understanding the impacts of biomass composition on BFI yield and quality can inform genetic engineering strategies to improve biochemical composition for biofuel production. In this work, wild type cyanobacterium Synechocystis sp. PCC 6803 biomass was doped with various common cellular storage compounds in lab-scale HTL experiments. Doping with glycogen or polyhydroxybutyrate (PHB) significantly reduced BFI yields, while doping with triglycerides (TAG) or medium chain-length polyhydroxyalkanoate (mcl-PHA) increased BFI yield and quality. In light of these observations, a genetically engineered Synechocystis strain deficient in glycogen biosynthesis was cultivated to produce biomass for HTL, leading to a 17% increase in BFI yield. In addition, we have built a multiphase component additivity (MCA) model that can predict BFI yield and quality with PHAs in the biomass. This work demonstrates an effective strategy to integrate strain development with downstream biomass conversion to maximize biofuel yield, with lessons applicable to microalgae as well as other biomass.

In order to mitigate ongoing effects of the climate change due to the use of fossil sources for the production of fuels and chemicals, strong efforts are necessary for gradually switch to renewable sources, thus improving circular carbon utilization. The transportation sector is one of the major contributors to global green-house gas (GHG) emissions and the CO2 generation is expected to grow due to increasing demand for transportation driven by growth in world population as well as economies for developing countries. Additionally, the integrated production of fuels and chemicals is nowadays a standard approach in petroleum refinery where 85% of the entire oil barrel is used for fuel production and the remaining 15% to produce chemicals, that account for about 50% of the overall profits. Thermochemical biorefineries for the conversion of lignocellulosic biomass are a promising route to produce precursors for fuels and chemicals for the transportation sector and chemical industry. However, technical challenges still need to be tackled to improve the thermochemical technologies through economically viable approaches for wider industrial applications. In this work, thermochemical conversion-based biorefineries for the valorization of lignocellulosic biomass were investigated to improve the process technologies toward industrial scale-up and commercialization. More in details, studies on the optimization of the thermochemical conversion process, pathway for co-products extraction and scale-up/commercialization routes were addressed for fast pyrolysis (FP) and hydrothermal liquefaction (HTL) biorefineries. In collaboration with the U.S. National Renewable Energy Laboratory (NREL), fast pyrolysis biorefinery for the conversion of lignocellulosic feedstock (e.g. forest residues) has been investigated through advanced approaches for process optimization and co-products extraction as well as the integration of bio-intermediates into existing petroleum infrastructures. Fast pyrolysis (FP) or catalytic fast pyrolysis (CFP) is a suitable process for the conversion of dry lignocellulosic sources through a thermal and catalytic cracking of the molecular structures. The process take place in absence of oxygen where the solid matrix composing the lignocellulosic biomass (cellulose, hemicellulose and lignin) is thermally cracked to form lighter compounds in form of vapors that are quickly condensed in order to maximize the liquid bio/oil percentage. Therefore, FP/CFP are efficient processes that leads to the production of high yields of liquid bio-oil (up to 80 wt.%). Raw bio-oil from FP has high oxygen content and high acidity as well as chemical instability from these properties that make it incompatible to be directly used as conventional fuels substitute or in blends. Thus, vapor or liquid upgrading is needed to improve the overall bio-oil quality and reduce the costs of final upgrading to fuel hydrocarbons. In this work, experimental studies have been carried out on micro-scale equipment and pilot plant, showing the possibility of preconditioning the FP vapors through a catalytic hot gas filter (CHGF) in order to partially deoxygenates the organic streams forming aromatic hydrocarbons, increasing the presence of valuable phenolics compounds as well as reducing the presence of unwanted corrosive compounds (such as carboxylic acids). Furthermore, the controlled fractional condensation of the partially upgraded vapors was used to validate the upgrading efficacy and to propose a separation pathway that has the potential of roughly concentrate interesting fraction for biorefinery co-products extraction. Thus, potential co-products pathway can be achieved through compounds separation directly from the vapor phase (e.g. through fractional condensation) or from the liquid phase (e.g. distillation or liquid-liquid extraction). In this regard, bio-based co-products from CFP biorefinery have been investigated, extracting organic molecules from pyrolysis liquid streams that can be used as bio-derived active ingredients in insecticides formulations. Fractions of CFP oil were obtained by vacuum distillation and then tested to evaluate the insecticidal activity. A correlation study between the dosage and the insect mortality…

Simple Ti imido halide complexes such as [Br2Ti(NtBu)py2]2 are competent catalysts for the synthesis of unsymmetrical carbodiimides via Ti-catalyzed nitrene transfer from diazenes or azides to isocyanides. This is the only example of catalytic nitrene transfer to isocyanides where diazenes have been employed as the nitrene source. Both alkyl and aryl isocyanides are compatible with the reaction conditions, although product inhibition with sterically unencumbered substrates sometimes limits the yield when diazenes are employed as the oxi-dant. The reaction mechanism has been investigated both experimentally and computationally, wherein a key feature is that product release is triggered by electron transfer from an η2-carbodiimide to a Ti-bound azobenzene. This ligand-to-ligand redox buffering obviates the need for high-energy formally TiII intermediates, and provides further evidence that substrate and product “redox noninnocence” can promote unusual Ti redox catalytic transformations.

Fast gas chromatography that leverages the high chromatographic efficiency of narrow bore capillary column technology and temperature programming was successfully integrated with a third-generation low void-volume, 3D-printed two-stage microreactor. Effective management of extra-column effect and the capability to perform post-column backflushing were achieved with the incorporation of a recently commercialized, electronically controlled pneumatic switching device and a deactivated metal three-way microdevice. With this configuration, narrow bore capillary columns having internal diameters between 100 µm to 150 µm can be employed to produce chromatographic peaks in the domain of fast gas chromatography, with peak widths at half-height ranging from 0.42 s to 0.92 s for probe compounds having k’ over a range from 1.7 for toluene to 60 with the last analyte (nC44) eluted in less than 12 min. The carbon independent response capability of the 3D-printed microreactor affords unique and advantaged differentiators, for instance, conducting measurement of the target analytes using one single carbon-containing compound for calibration with an acceptable accuracy of ±10%, achieving a higher degree of accuracy by eliminating the need for multi-level and multi-compound calibration, and improving sensitivity for compounds that are not efficiently ionized by flame ionization detection. Using this platform, repeatability of retention times for 14 probe compounds was less than 0.1 % RSD (n = 10), and less than 1.0 % RSD (n = 10) for area counts. The utility of the analytical approach was illustrated with relevant, challenging applications.

A 3D-printed microreactor for post-column reaction was successfully integrated with comprehensive two-dimensional gas chromatography. A two-stage post-column reaction provided carbon independent response, it enhanced flame ionization detection uniformity, and it improved detector sensitivity. These enhancements are critical to overcome challenges in analyses using comprehensive two-dimensional gas chromatography and flame ionization detection, which aim to separate and quantify multiple components. Post-column reaction flame ionization detection eliminated the requirement of multi-level and multi-compound calibration, it enabled determination of target analytes with a single carbon-containing calibration compound with an accuracy of ±10%, and it improved sensitivity for compounds that were not efficiently ionized by flame ionization detection. Extra column band-broadening caused by the incorporation of the 3D-printed microreactor was minimized using optimized reactor operating parame-ters and inter-column connectivity. Chromatographic fidelity was in the practical domain of comprehensive two-dimensional gas chromatography. Typical peak widths at half-height using the described approach ranged from 165 ms to 235 ms for probe com-pounds with retention factors spanning 5 < k < 40.

Despite the ubiquity of reports describing titanium (Ti)-catalyzed [2 + 2 + 2] cyclotrimerization of alkynes, the incorporation of arynes into this potent manifold has never been reported. The in situ generation of arynes often requires fluoride, which instead will react with the highly fluorophilic Ti center, suppressing productive catalysis. Herein, we describe the use of group 4 diarylmetallocenes, CpR2MAr2 (CpR = C5H5, C5Me5; M = Ti, Zr), as aryne precursors for the Ti-catalyzed synthesis of substituted naphthalenes via coupling with 2 equiv of an alkyne. Fair-to-good yields of the desired naphthalene products could be obtained with 1% catalyst loadings, which is roughly an order of magnitude lower than similar reactions catalyzed by palladium or nickel. Additionally, naphthalenes find broad applications in the electronics, photovoltaics, and pharmaceutical industries, urging the discovery of more economic syntheses. These results indicate that aryne transfer from a CpR2M(η2-aryne) complex to another metal is a viable route for the introduction of aryne fragments into organometallic catalytic processes.

Specifying effective analytical techniques and methods can be very challenging when a large number of sample streams need to be analyzed with high frequency. Combining those requirements with the need to monitor multiple components over a wide range of concentrations makes at-line analytical approaches preferred by many analytical scientists. Traditionally, at-line analytical support requires sample preparation and operator time. Recently developed technologies enabled automated sample preparation tools coupled with gas chromatography; thus, eliminating sample preparation steps and increasing productivity. Recently a commercial micro-reactor was introduced that can be combined with a flame ionization detector, providing the ability to quantify components without the need to perform a standard calibration, which saves significant time and materials. In this manuscript, we describe a unique analytical capability that combines automated sample preparation and gas chromatography with flame ionization detection and universal carbon response to provide high flexibility and accuracy when there is minimal information about the unknowns or reference materials are not available. Some of the challenges and performance monitoring techniques for this technology are also discussed in this manuscript.

The copolymerization of vinyl benzyl alcohol (VBA) and carbon monoxide (CO) to give a new polyester poly(VBA-CO) has been achieved via palladium-catalyzed hydroesterification. Reaction conditions involve moderate temperatures, moderate to low CO pressures, and low catalyst loadings to give a low molar mass (Mn ∼ 3–4 kg/mol) polymer as a ∼2:1 mixture of linear to branched repeat units. The polymer molar mass increase is consistent with a step-growth polymerization mechanism, and ester yields of >97% are achieved within 24 h. However, increases in Mn cease beyond 16 h. Control experiments indicate that the degree of polymerization is limited due to a combination of side reactions such as alcoholic end-group oxidation, hydroxycarbonylation, and alcohol acetylation, which lead to the degradation of monomeric and polymeric end groups. When a less promiscuous substrate is used such as 10-undecenol, higher molar masses (Mn ∼ 16 kg/mol) are achieved. This method has the potential to be a mild route to new polyester architectures with appropriate mitigation of side reactions.

Metal oxide-filled reactors constructed with ceramic tubes or fused silica capillary are widely used for combustion in gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS). However, they tend to be easily cracked or broken and prone to leaks at operating temperatures of ∼950 °C. Here we introduce a modified commercially available catalytic combustion/reduction methanizer to quantitatively convert organics to CO2 for δ13C analysis while retaining chromatographic resolution. These modified “ARC” reactors operate with a transition-metal catalyst that requires a flowing O2 gas to enable complete conversion to CO2 at lower temperature (620 °C) with acceptable reactor life, reduced complexity, and improved robustness. Performance of two versions of the ARC reactors with different combustion volumes was characterized by analysis of steroid and alkane isotopic standard materials. Linearity of steroid isotopic standards ranged from 0.02 to 0.60 ‰/V in the range of 25 to 200 ng of each steroid injected. Precisions and accuracies of measurements for steroids and alkanes had average standard deviations of SD(δ13C) less than ±0.18 ‰ and average accuracy of better than 0.19 ‰ δ13CVPDB. Peak width expansion within both devices were similar to that in traditionally used metal oxide reactors. These data demonstrate for the first time that novel combustion schemes enable operation at lower temperatures as an alternative approach comparable to high temperature techniques to yield high precision δ13C data with GCC-IRMS.

The first part of this chapter presents the main objectives for performing derivatization of a sample to be analyzed by gas chromatography (GC) or gas chromatography/mass spectrometry (GC/MS). The derivatization is typically done to change the analyte properties for a better separation and also for enhancing the method sensitivity. In GC/MS, derivatization may improve the capability of compound identification. Examples illustrating such improvements are included. The second part describes several types of derivatization that are more frequently used in analytical practice. These include alkylation (e.g., methylation), formation of aryl derivatives, silylation (e.g., formation of trimethylsilyl derivatives), acylation (e.g., reactions with acyl chlorides or with chloroformates), and several other types of derivatizations. The chapter also presents typical derivatizations for analytes with specific functional groups and discusses artifact formation in certain derivatization reactions.

A reliable and practical approach for the direct measurement of volatile oxygenated compounds in high pressure liquefied light hydrocarbons has been successfully developed. The approach incorporates the use of a pressurized liquid injection device for sample introduction, a highly selective and polar ionic sorbent column technology to achieve separation of the targeted oxygenated compounds, and the augmentation of a recently commercialized dual-stage post column microreactor to convert carbon compounds; first to carbon dioxide by combustion and subsequently to methane by methanation. This two-stage conversion strategy is highly advantageous as it enables carbon compound independent response as well as sensitivity improvements, particularly for short-chain oxygenated compounds. Oxygenated compounds such as acetaldehyde, propionaldehyde, methanol, ethanol, iso-propanol, n-propanol, and acetone in light hydrocarbons were found to have respectable linear ranges from 0.1 ppm (v/v) to 3,000 ppm (v/v) with R2 greater than 0.997 and a relative precision of less than 10% RSD (n = 7). With the incorporation of carbon compound independent response capability, one single carbon-containing compound can be used for calibration to measure any of the target analytes with a respectable accuracy of less than ±10% error. The unique feature of carbon equimolar response also enables the possibility of determining a “total” concentration for the known volatile oxygenated compounds. As well, the need for multi-level calibration was eliminated over the range of interest. This novel concept enables new measurement capability and flexibility, enhances analytical throughput, and substantially decreases the overall cost of ownership. The utility of the methodology was demonstrated with practical industrial applications.

Methylbenzenes entrained within the cavities of silicoaluminophosphate zeotype HSAPO-34 react with methanol in H+-mediated dealkylation to give ethylene and propylene in methanol-to-olefins catalysis. Methylbenzenes dealkylation on solid acids is proposed to occur either via the side-chain mechanism, where an exocyclic CC undergoes successive methylation prior to CC cleavage for olefin elimination, or the paring mechanism, where ring contraction to a bicyclohexenyl cation precedes CC cleavage for olefin elimination. Distinct dealkylation mechanisms prescribe distinct combinations of C atoms—from aromatic methyl, aromatic ring, and methanol/dimethyl ether—to comprise the olefin product. Site-specific isotope tracing that distinguishes between isotope labels in aromatic methyl and aromatic ring positions for each methylbenzene shows that tetramethylbenzene gives ethylene via the side-chain mechanism and penta- and hexamethylbenzene give propylene via the paring mechanism. The ratio of propylene selectivity to ethylene selectivity increases in methanol reactions on HSAPO-34 entrained with a distribution of methylbenzenes deliberately manipulated towards increasing fractions of penta- and hexamethylbenzene, corroborating the conclusion that aromatic precursors and dealkylation mechanisms for ethylene diverge from those for propylene.

A gas chromatographic strategy to advance the direct detection and quantification of volatile aliphatic aldehydes such as formal-dehyde and acetaldehyde in gas phase matrices without the need for sample pre-treatment or concentration has been successfully developed. The catalytic hydrogenolysis of aldehydes to alkanes is conducted in-situ within the 3D printed steel jet assembly of the flame ionization detector and without any additional hardware required. Reliable conversion efficiencies of greater than 90% with respectable peak symmetries for the analytes were attained at 400 °C. Quantification of formaldehyde and acetaldehyde at parts-per-million level over a range of 0.5-300 ppm (v/v) for formaldehyde and 0.2-430 ppm (v/v) for acetaldehyde with a respect-able precision of less than 5% RSD (n = 10) was achieved. Total analysis time is less than 10 min. Linearity with a correlation coef-ficient of R2 greater than 0.9997 and measured recoveries of >99% for spike tests under the specified conditions were achieved. The 3D printed steel jet assembly was found to be reliable and resilient to matrices such as air, water, hydrocarbons, and aromatics. An additional benefit realized with this analytical strategy is that the slight restriction induced by the presence of the catalyst in the 3D printed jet assembly enables backflush via the inlet split vent without the need for additional pressure control and inter-column connection devices. The utility of this technique was demonstrated with important aldehyde applications from various segments.

Medium chain-length linear α-olefins (mcl-LAO) are versatile precursors to commodity products such as synthetic lubricants and biodegradable detergents, and have been traditionally produced from ethylene oligomerization and Fischer–Tropsch synthesis. Medium chain-length polyhydroxyalkanoic acid (mcl-PHA) can be produced by some microorganisms as an energy storage. In this study, Pseudomonas putida biomass that contained mcl-PHA was used in HTL at 300 °C for 30 min, and up to 65 mol% of mcl-PHA was converted into mcl-LAO. The yield and quality of the bio-oil co-produced in the HTL was remarkably improved with the biomass rich in mcl-PHA. Experiments with extracted mcl-PHA revealed the degradation mechanism of mcl-PHA in HTL. Overall, this work demonstrates a novel process to co-produce mcl-LAO and bio-oil from renewable biomass.

In the current study, low-density polyethylene and polystyrene were co-pyrolyzed with dealkaline lignin in a micro-reactor at 500°C with and without low-cost red clay catalyst. The products were analyzed with GC-MS/FID to quantify phenolic compounds, alkanes and alkenes. The synergistic effect between plastics and lignin was studied by comparing the carbon yield of compounds from co-pyrolysis with that from individual pyrolysis. The co-pyrolysis of lignin and polystyrene was also performed at 600, 700 and 800°C to examine the effect of pyrolysis temperature. The study explores a novel approach to enhance lignin depolymerization with red clay catalyst while utilizing waste plastics.

Quantification of complex carbon‐containing mixtures are typically very time‐intensive tasks with regards to the calibration process. A gas chromatograph with a flame ionization detector yields strong responses to organic compounds and provides a wide linear range over many orders of magnitude; however, responses for highly functionalized and heteroatom containing compounds can be variable. Here, a commercial Polyarc microreactor unit, placed before the flame ionization detector, was investigated as a means of normalizing carbon response across all compounds. The device includes two catalytic reaction chambers, ultimately evenly converting all carbon atoms to methane for flame ionization detection. Three groups of different complex mixtures from n‐alkane to terpene and polymer mixtures were analyzed to evaluate the potential for calibration‐free quantitation of the new detector arrangement. We have obtained accurate quantification results without time‐consuming calibration processes. The quantification of a terpene mixture and a polymer mixture confirm the ability of the detector for analyzing samples that either have complex physical or structural properties or wide concentration range. In summary, compared to other detectors, this methanizer – flame ionization detection system provides a simplified workflow, which can eliminate calibration steps and increase throughput.

Comprehensive two-dimensional gas chromatography (GC×GC) has impacted the workflow of GC-based methods used in petroleum industry. Application of GC×GC to petroleomic investigations have guided sample preparation to faster, cleaner, and more reliable formats. For instance, solvent consumption has been drastically reduced when using miniaturized devices in routine applications. Furthermore, flow-modulation has enabled cost-effective analysis and powerful separations of gases, fuels, and crude oils. Hyphenation of GC×GC to conventional and high resolution mass spectrometry has enabled the detection and identification of hundreds of compounds in a single analysis. Pixel-based methods enabled efficient handling of big data generated by GC×GC in forensic and geochemical investigations. This review has highlighted an ever-growing demand for modern and powerful analytical methods for oil & gas industry. Here, we described the most recent advances to sample preparation, GC×GC instrumentation, and multivariate data analysis in petroleum industry, including microextractions, high temperature GC×GC, and pixel-based data analysis.

An analytical technique that employs in-situ methanation with flame ionization detection for the measurement of carbon dioxide in various matrices has been developed and implemented. The methanation of carbon dioxide to methane is conducted in-situ within the 3D printed jet of the flame ionization detector without any additional hardware required. Quantification of carbon dioxide at the parts-per-million level over a range of 1-10,000 ppm (v/v) with respectable precision of less than 5% RSD (n = 10) was achieved. Total analysis time is less than 6 min. Linearity with a correlation coefficient of R2 = 0.9995 and a measured recovery of >99% under the specified conditions were achieved. Leveraging the additional back pressure generated by the modified jet assembly, a novel strategy of post-column backflushing with the detector fuel gas was successfully innovated to provide advantaged synergy in enhanced reliability and throughput of the analytical system. This backflushing approach had no known negative impact on conversion efficiency or performance of the jet assembly.The utility of this technique was demonstrated with relevant carbon dioxide applications in various sectors including carbonated beverage, environmental, and chemical industries.

The flame ionization detector (FID) is a robust tool in gas chromatography (GC) due to its sensitivity and linear response in the detection of common organic compounds. However, FID response to oxygenated or highly functionalized organic molecules is low, or in some cases non-existent, making it difficult or impossible to detect and quantify some organic compounds. In this work, the combination of a GC/FID system with a catalytic microreactor, which performs post-column combustion–methanation to convert organic compounds to methane, is shown to be an effective approach for quantifying low-response organic compounds. Molecules that were previously undetectable by conventional FID, including carbon monoxide and carbon dioxide, respond with the same high response of methane in the FID. Low-response molecules, including formaldehyde, formic acid, formamide, and ten other oxygenates also demonstrated enhanced detector response equivalent to that of methane in the FID. The linear response of the FID to these molecules and the equivalent sensitivity to methane indicate that accurate quantification is possible without the usual calibration-corrections (e.g., response factors or correction factors) to the FID response.

Scope of Review. Analysis of volatile and semi-volatile analytes by gas chromatography (GC) methods is an indispensable tool in the analytical chemist’s tool box. A myriad of fields of study rely upon the application of GC methods to address an ever growing demand to provide useful chemical information from GC data. As the realm of GC application has expanded, there has been an evolution to develop more powerful instrumental and data analysis approaches to keep pace with the wealth of complex samples that require analysis. To address this challenge, advances in GC instrumentation having evolved from one-dimensional gas chromatography (1D-GC) and heart cutting approaches such as (GC-GC), to instrumentation referred to broadly as multidimensional gas chromatography (MDGC), which can take on many forms. The principle form of MDGC that has gained wide implementation is comprehensive two-dimensional (2D) gas chromatography (GC × GC) as shown in Figure 1A, pioneered nearly 26 years ago by Liu and Phillips.1 When comparing 1D-GC (Figure 1B) relative to GC × GC (Figure 1C), the benefits of a secondary separation become evident. Blumberg and co-workers have theoretically determined that the 2D peak capacity provided by GC × GC compared to the peak capacity of 1D-GC is approximately an order of magnitude higher when the run times are held constant.2 This benefit is illustrated using a relatively complex sample of coffee. By adding a multivariate detector such as a time-of-flight mass spectrometry (TOFMS), another selective dimension of data is provided which may allow identification of analytes (Figure 1D). This review will focus essentially on GC × GC, with selected developments of other forms of MDGC also covered. In this regard, we focus primarily on research published since the last Fundamental Review published by Seeley and Seeley in 2013,3 with older publications covered as deemed necessary to provide additional insight into addressing the current challenges, and to put the more recent developments into historical context.

The Brønsted acid site densities of ZSM-5, BEA and single unit cell self-pillared pentasil (SPP) zeolites of varying Si/Al ratios were measured using a new technique, reactive gas chromatography (RGC), which utilizes alkylamine decomposition to selectively count Brønsted acid sites. Reactive gas chromatography condenses the conventional temperature-programmed desorption mass spectrometer (TPD-MS) setup into a single, fully-automated gas chromatograph (GC). Alkylamine decomposition reactions were conducted in a microcatalytic reactor placed within a temperature-controlled GC inlet liner. Products were then separated in a GC column and quantified with a flame ionization detector. A comparison between reactive gas chromatography measurements and conventional temperature programmed desorption methods showed agreement; RGC acid site density measurements were further confirmed by comparison with in situ pyridine titration of isopropanol dehydration. Reactive gas chromatography measurements performed using multiple alkylamines, were found to yield identical Brønsted acid site densities. The method of reactive gas chromatography was found to be highly sensitive, where siliceous materials with Brønsted acid site densities as low as ~1.0 μmol gcat-1 could be reliably measured.

While laboratories utilize many approaches to calibrate analytical assays, they always involve the analysis of one or more calibrators that have known levels of the analyte of interest. The response of the analyte of interest in test samples is directly or indirectly compared to the response of the same analyte in the calibrators to determine the concentration of the analyte in the test sample. Analyte calibration is burdened with limitations and potential bias: Calibrator preparation inherently contains a level of inaccuracy, which propagates to the quantitation of any unknown based on that calibration. Even small biases in the calibration will impact the quantitative accuracy of samples.

Quantitative analysis of complex mixtures containing hundreds-to-thousands of organic compounds rich in heteroatoms, including oxygen, sulfur, and nitrogen, is a major challenge in the fuel, food, and chemical industries. In this work, a two-stage (oxidation and methanation) catalytic process in a 3D-printed metal microreactor was evaluated for its capability to convert sulfur-containing organic compounds to methane. The microreactor was inserted into a gas chromatograph between the capillary column and flame ionization detector. Catalytic conversion of all sulfur-containing analytes to methane enabled carbon quantification without calibration, by the method identified as “quantitative carbon detection” or QCD. Quantification of tetrahydrothiophene, dimethyl sulfoxide, diethyl sulfide, and thiophene indicated complete conversion to methane at 450°C. Long-term performance of a commercial microreactor was evaluated for 2,000 consecutive injections of sulfur-containing organic analytes. The sulfur processing capacity of the microreactor was identified experimentally, after which reduced conversion to methane was observed.

Catalytic ring-opening dehydration of tetrahydrofuran (THF), itself a product of decarbonylation and reduction of biomass-derived furfural, yields 1,3-butadiene, an important monomer in rubbers and elastomers. It is demonstrated that dehydra-decyclization of THF with phosphorus-containing siliceous self-pillared pentasil (SPP) or MFI structure exhibits high selectivity to butadiene (85–99%) at both low (9%) and high (89%) conversion of THF. High selectivity to pentadiene and hexadiene was also obtained from 2-methyl-tetrahydrofuran and 2,5-dimethyl-tetrahydrofuran, respectively, with phosphorus-containing, all-silica zeolites.

Catalytic hydrogenation of itaconic acid (obtained from glucose fermentation) yields 3-methyl-tetrahydrofuran (3-MTHF), which then undergoes catalytic dehydra-decyclization to isoprene. It is demonstrated that a one-pot cascade reaction converts itaconic acid to 3-MTHF at ∼80% yield with Pd–Re/C catalyst and 1000 psig H2. Subsequent gas-phase catalytic ring opening and dehydration of 3-MTHF with phosphorus-containing zeolites including P-BEA, P-MFI, and P-SPP (self-pillared pentasil) exhibits 90% selectivity to dienes (70% isoprene, 20% pentadienes) at 20–25% conversion.

Analysis of trace compounds, such as pesticides and other contaminants, within consumer products, fuels, and the environment requires quantification of increasingly complex mixtures of difficult-to-quantify compounds. Many compounds of interest are non-volatile and exhibit poor response in current gas chromatography and flame ionization systems. Here we show the reaction of trimethylsilylated chemical analytes to methane using a quantitative carbon detector (QCD; the Polyarc reactor) within a gas chromatograph (GC), thereby enabling enhanced detection (up to 10×) of highly functionalized compounds including carbohydrates, acids, drugs, flavorants, and pesticides. Analysis of a complex mixture of compounds shows that the GC-QCD method exhibitsfaster and more accurate analysis of complex mixtures commonly encountered in everyday products and the environment.