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Secondary organic aerosols (SOA), formed through the gas-phase oxidation of volatile organic compounds (VOCs), can reside in the atmosphere for many days. The formation of SOA takes place rapidly within hours after VOC emissions, but SOA can undergo much slower physical and chemical processes throughout their lifetime in the atmosphere. The acidity of atmospheric aerosols spans a wide range, with the most acidic particles having negative pH values, which can promote acid-catalyzed reactions. The goal of this work is to elucidate poorly understood mechanisms and rates of acid-catalyzed aging of mixtures of representative SOA compounds. SOA were generated by the ozonolysis of α-pinene in a continuous flow reactor and then collected using a foil substrate. SOA samples were extracted and aged by exposure to varying concentrations of aqueous H2SO4 for 1-2 days. Chemical analysis of fresh and aged samples was conducted using ultra-performance liquid chromatography coupled with photodiode array spectrophotomety and high-resolution mass spectrometry. In addition, UV-vis spectrophotometry and fluorescence spectrophotometry were used to examine the changes in optical properties before and after aging. We observed that SOA that aged in moderately acidic conditions (pH from 0 to 4) experienced small changes in composition, while SOA that aged in a highly acidic environment (pH from -1 to 0) experienced more dramatic changes in composition, including the formation of compounds containing sulfur. Additionally, at highly acidic conditions, light-absorbing and fluorescent compounds appeared, but their identities could not be ascertained due to their small relative abundance. This study shows that acidity is a major driver of SOA aging, resulting in a large change in the chemical composition and optical properties of aerosols in regions where high concentrations of H2SO4 persist, such as upper troposphere and lower stratosphere.

Sulfamic acid functionalized polyvinyl chloride catalysts (PVC-N-SO3H, N = EDA, DTA, TTA, TPA, PHA) were prepared as efficient heterogeneous solid acid catalysts via two-step treatment processes. The prepared catalysts were characterized by X-ray diffraction analysis (XRD), TG thermograms/derivative thermogravimetric (TG/DTG), transmission electron microscope (TEM), elemental mappings and energy-dispersive spectroscopy analyses (STEM-EDS), and FTIR measurements (FTIR) as well as acid–base back-titration. The acetalization of aldehydes (ketones) and alcohols to acetal (ketal) was selected to evaluate the acid catalytic performance of PVC-N-SO3H. The results showed that PVC-EDA-SO3H exhibit excellent activity and reusability due to its highly exposed sulfonic acid sites, high surface acid density (2.28 mmol g−1) for the conversion of aldehydes (ketones) to acetal (ketal). This new solid acid has obvious advantages in reusability and catalytic activity over traditional homogeneous concentrated sulfuric acid and heterogeneous sulfonated resin catalysts. Furthermore, PVC-EDA-SO3H exhibited an excellent catalytic performance in the synthesis of 12 acetals (ketals) as well as a good compatibility in the hydroxyalkylation of phenol with formaldehyde to bisphenol F (BPF) and the esterification reaction of oleic acid and methanol to biodiesel. More importantly, it could also be recovered easily and used repeatedly at least nine times without an obvious decrease in the activity. [ABSTRACT FROM AUTHOR]

In this work, a 3D printing method, robocasting was utilized to manufacture zeolite ZSM-5-based woodpile monolith catalysts of approximately 10-mm diameter, using bentonite clay as binding matrix. The effect of three different binder concentrations, in the 40–60 wt.% range, on the rheological, physicochemical, and mechanical properties was examined. The rheometer measurements showed that the printing pastes have identical shear thinning behavior and demonstrate sufficient storage modulus, irrespective of the binder concentration. The printed monoliths had high BET surface areas and porosity. The results showed that the ZSM-5 crystals retained their porous structure, textural characteristics, and crystalline structure during the additive manufacturing process. Pyridine FTIR measurements demonstrated reduced total acidity and number of Brønsted acid sites in the final specimens due to the dilution with the bentonite powder. However, the acidity reduction was roughly proportional to the binder concentration, signifying that the ZSM-5 crystallites also retain their acidity during the robocasting printing. Finally, the mechanical reliability of the thermally treated monoliths was determined by calculating the Weibull modulus values through linear regression of the Weibull equation. The increase in the binder concentration increased the compression strength by a factor of 4.5 and achieved superior mechanical reliability. [ABSTRACT FROM AUTHOR]

The Biginelli Reaction is a one-pot acid catalyzed cyclocondensation of -keto ester, urea and aromatic aldehyde which leads to the synthesis of functionalized 3,4-dihydro-2(H)-pyrimidinones (DHPMs). These DHPMs (synthetic and natural) possess a wide range of pharmacological activities. A simple, efficient, and cost-effective method for the synthesis of 3,4-dihydropyrimidin-2(1H)-one by a one-pot three-component cyclocondensation reaction of a 1,3-dicarbonyl compound, an aldehyde and urea using HCl as catalyst is reported. The three-component condensation of an aldehyde, a -keto ester and urea in the presence of a catalytic amount of HCl, 3,4-Dihydropyrimidin-2(1H)-ones were synthesized in high yields. Recently much attention has been devoted towards dihydropyrimidine derivatives due to their significant therapeutic and medicinal properties. All the products in reaction obtained in good to very good yields by proceeding through a simple and efficient procedure. All the synthesized compound’s structure has been established by advanced spectroscopic data (FTIR, 1HNMR, and 13CNMR) and evaluated for their antibacterial activity against two types of bacteria (S. aureus and E.coli).

BACKGROUND The synthesis of solid acid catalysts of recoverable and environmentally friendly nature has gained increasing attention in recent years. The distribution of Brønsted and Lewis acidic sites on the surface of sulfated metal oxides determines the catalytic performance, which is affected by many key factors, such as the concentration of sulfuric acid impregnated and the morphology of the metal oxides used. In this study, TiO2 nanosheets were successfully synthesized and used as carrier for the preparation of solid acid catalysts. RESULTS: The concentration of sulfuric acid for the impregnation resulted in various distributions of Brønsted and Lewis acidic sites on the surface of sulfated TiO2. With a medium concentration of sulfuric acid (1 mol L−1) for the impregnation, the highest ratio of Brønsted to Lewis acidic sites can be achieved, and the catalyst showed superior catalytic activity for the conversion of furfuryl alcohol (FA) to ethyl levulinate (EL) in ethanol and the conversion of fructose to 5‐hydroxymethylfurfural (HMF) in dimethyl sulfoxide (DMSO). CONCLUSION: The sulfation of TiO2 nanosheets induced the formation of both Brønsted and Lewis acidic sites. The Brønsted acidic sites were more effective for catalyzing the conversion of FA or fructose. The poor recyclability of the 1.0‐SO42−/TiO2 catalyst in the conversion of FA to EL in ethanol, a protic solvent, was due to the leaching of sulfur species. The deactivation of the catalyst in DMSO was due to coking, which could be resolved via calcination of the coke species in air. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The solution-phase stability of the hydronium ion catalyst significantly affects the rates of acid-catalyzed reactions, which are ubiquitously utilized to convert biomass to valuable chemicals. In this work, classical molecular dynamics simulations were performed to quantify the stability of hydronium and chloride ions by measuring their solvation free energies in water, 1,4-dioxane (DIOX), tetrahydrofuran (THF), γ-valerolactone (GVL), N-methyl-2-pyrrolidone (NMP), acetone (ACE), and dimethyl sulfoxide (DMSO). By measuring the free energy for transferring a hydronium ion from pure water to pure organic solvent, we found that the hydronium ion is destabilized in DIOX, THF, and GVL and stabilized in NMP, ACE, and DMSO relative to water. The distinction between these organic solvents can be used to predict the preference of the hydronium ion for specific regions in aqueous mixtures of organic solvents. We then incorporated the stability of the hydronium ion into a correlative model for the acid-catalyzed conversion of 1,2-propanediol to propanal. The revised model is able to predict experimental reaction rates across solvent systems with different organic solvents. These results demonstrate the ability of classical molecular dynamics simulations to screen solvent systems for improved acid-catalyzed reaction performance.

1,1-Bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane (TMCH), an industrial initiator and cross-linking agent comprising two active peroxy bonds, becomes unstable when specific acids—namely phosphoric acid (H3PO4), sulfuric acid (H2SO4), nitric acid (HNO3), or hydrochloric acid (HCl)—are added to it. The incompatible reactivity of TMCH with these specific acids was monitored through differential scanning calorimetry (DSC) and thermal activity monitor III (TAM III). Thermophysical parameters, including exothermic onset temperature, decomposition heat, and peak temperature, were estimated through DSC dynamic testing to obtain the exothermic ranking. Isothermal testing was conducted using TAM III to estimate the thermokinetic parameters of the mixture of TMCH and a specific acid. A high reaction enthalpy was observed when TMCH was mixed with H2SO4, HNO3, or HCl due to the characteristic acid-catalyzed reactions. Furthermore, HCl initiated an earlier onset temperature for TMCH decomposition, and the mixtures of TMCH with HNO3 and HCl presented multiple thermal curves with complex exothermic peaks. In summary, the thermokinetic parameters and reaction models of TMCH with specific acids were evaluated to classify the runaway potential. [ABSTRACT FROM AUTHOR]

The acid-catalyzed reaction of (Z)- and (E)-B-nor-5,10-seco-ketones 2 and 3 resulted in an intramolecular cyclization to give the 5-hydroxy-A-nor-1b,5b-10(19)-methylidene derivative 8, the 5b-hydroxy-A-nor-1(10)-unsaturated compound 9 and the 5b,10a-dihydroxy-A-nor-product 10, from the (Z)-isomer and the 5-hydroxy-A-nor-1a,5b-10(19)-methylidene product 11, from the (E)-isomer. Upon UV-irradiation, the (Z)- and (E)-seco-ketones 2 and 3 underwent a reversible (Z)/(E) and (E)/(Z)-isomerization and in addition to a transannular photocyclization to afford the 10(19)-methylidene derivatives 8 and 11, respectively, while photolysis of the 10(19)-methylidene-B-nor-5,10-seco-ketone 4 gave the oxetane derivative 12.

The acid-catalyzed reaction of (Z)- and (E)-B-nor-5,10-seco-ketones 2 and 3 resulted in an intramolecular cyclization to give the 5-hydroxy-A-nor-1β,5β-10(19)-methylidene derivative 8, the 5β-hydroxy-A-nor-1(10)-unsaturated compound 9 and the 5β,10β-dihydroxy A-nor-product 10, from the (Z)-isomer and the 5-hydroxy-A-nor-1β,5β-10(19)-methylidene product 11, from the (E)-isomer. Upon UV-irradiation, the (Z)- and (E)-seco-ketones 2 and 3 underwent a reversible (Z)/(E) and (E)/(Z)-isomerization and in addition to a transannular photocyclization to afford the 10(19)-methylidene derivatives 8 and 11, respectively, while photolysis of the 10(19)-methylidene-B-nor-5,10-seco-ketone 4 gave the oxetane derivative 12.

Structural architecture and unique physical, chemical, thermal, and mechanical properties of ordered mesoporous silica materials can be tuned. High flexibility of silica materials can provide good support for different metal nanoparticles, metal oxides, and organic functional groups. The properties of silica materials can vary to a great extent by introducing the optimum amount of metal species co-doped, dispersed or composites with the silica mesostructure. The present study investigates the deposition of CeIII/IV/CeO2 on the silica surface by using different wet chemical engineering methods, illustrates the syntheses of those ceria-silica or metal doped ceria-silica nanomaterials and offers clear picture of the influence that incorporated ceria concentration has on the properties of the support material. Ceria-silica based ordered mesoporous materials can have numerous applications is also discussed in this article, emphasizing its use as a heterogeneous catalyst in particular. [ABSTRACT FROM AUTHOR]

The synthesis and catalytic activity of a new sulfonic acid-functionalized periodic mesoporous organosilica (PMO) obtained by an in situ oxidation process have been reported. This material was prepared by co-condensation of a homemade thiol-functionalized bis-silane precursor (EtO) 3 Si-R-Si(OEt) 3 (R = CH 2 CHSH) with 1,2-bis(triethoxysilyl)ethane (BTEE) in the presence of a nonionic triblock co-polymer. Thiol groups were oxidized either in situ during the formation of the mesostructure, or by a post-synthesis oxidation of the solid material. The in situ generated sulfonated PMO material had a well-ordered hexagonal mesoporous structure and a narrow pore size distribution. The sulfonic acid concentration of these materials was in the range of 0.85–1.48 mmol H + g −1 . The catalytic performance of these sulfonic acid-functionalized materials was evaluated and compared with the commercial resin Amberlyst-15 in the esterification of acetic acid with benzyl alcohol. The in situ sulfonated PMO has shown to be an efficient, robust, and recyclable catalyst in acid-catalyzed reactions throughout consecutive catalytic cycles. [ABSTRACT FROM AUTHOR]

Novel biomass-derived porous carbons are attractive candidates for the preparation of carbon-supported catalysts with a wide range of catalytic applications. Such carbonaceous catalysts are environmentally benign and could provide a cost-competitive advantage as compared to existing heterogeneous catalysts. Tunable surface properties of carbon materials and excellent physical properties (e.g., hydrophobicity, chemically inert nature, etc.) are compatible with diverse catalysis reactions including organic transformations, as well as electro- and photochemical processes in aqueous solutions. This contribution provides an overview on the utilization of different biomass feedstocks and/or biomass-derived precursors for the synthesis of carbonaceous materials to design advanced catalytic systems and their emerging applications in catalysis. [ABSTRACT FROM AUTHOR]

Diels–Alder reactions of five-membered heterocycles containing one heteroatom with an N -arylmaleimide were studied. Cycloaddition of 2,5-dimethylfuran ( 4 ) with 2-(4-methylphenyl)maleimide ( 3 ) in toluene at 60 °C gave bicyclic adduct 5 . Cycloadditions of 3 with 2,5-dimethylthiophene ( 11 ) and 1,2,5-trimethylpyrrole ( 14 ) were also studied. Interestingly, the bicyclic compound 5 cleanly rearranged, with loss of water, when treated with p -toluenesulfonic acid in toluene at 80 °C to give 4,7-dimethyl-2- p -tolylisoindoline-1,3-dione ( 6 ). [ABSTRACT FROM AUTHOR]

Abstract: To understand the sources and formation processes of atmospheric carbonaceous aerosols in rural and mountainous areas of South China, an intensive measurement campaign was conducted at the summit of Mount Heng (27°18′N, 112°42′E, 1269 m asl) during the spring of 2009. The observed average concentrations of organic carbon (OC) and elemental carbon (EC) were 3.01 ± 2.2 and 0.54 ± 0.3 μg m−3, respectively. The total carbonaceous aerosols (TCA) averagely contributed to 20.7% of PM2.5. High OC/EC ratios (range: 1.6–10.4; average: 5.2 ± 1.8) were observed, suggesting the transport and secondary origins of the carbonaceous aerosols at Mount Heng. The amount of secondary organic carbon (SOC) was estimated using the EC-tracer method and accounted for 53.9% of the total OC on average. Good correlations were found between SOC and droplet-mode sulfate, and oxalate and droplet-mode sulfate, indicating the occurrence of in-cloud secondary organic aerosol (SOA) formation at Mount Heng. The concentrations of SOC and water soluble organic acids also displayed positive relationship with aerosol acidity, suggesting the enhancement of SOC formation by acid-catalyzed heterogeneous reactions. Backward trajectory analysis revealed that the observed aerosols at Mount Heng were predominantly associated with the air masses from the Pearl River Delta region (PRD) and Eastern China, which brought significant amounts of anthropogenic pollutants to the site. In addition, strong signals of biomass burning (elevated carbonaceous concentrations, OC/EC ratios and K+ concentrations) were observed in air masses from Southeast Asia, demonstrating that the biomass burning emissions in Southeast Asia could reach the boundary layer of South China and affect the air quality there during the spring season. [Copyright &y& Elsevier]

A reaction network for acid-catalyzed hydrocarbon hydroprocessing in the C2 to C12 range has been generated, as part of a larger work to model a naphtha hydrocraking unit at the elementary step level. The structure of the feedstock molecules is stored as Boolean matrixes, facilitating their mathematical manipulation according to the rules of each elementary reaction step during the reaction network generation. Detailed algorithms and examples are shown for every elementary reaction step. Acyclic and cyclic species are considered, up to two fused aromatic, olefinic or naphthenic rings. Besides conventional elementary reactions, algorithms for aromatic isomerization (methyl and ethyl migration) and dealkylation were developed. It must be highlighted that the complexity of the reaction network should be weighed against the available chromatographic data resolution. Therefore, mathematical restrictions might be added to the generated structures, such as maximum number of ramifications or maximum molecule size within a group of isomers. A sensitivity analysis of these restrictions was carried out, to determine their impact on the dimension of the generated reaction network. [ABSTRACT FROM AUTHOR]

Abstract: Particle in-situ pH (pH IS), defined as pH of the aqueous phase on aerosols, is an important factor in influencing aerosol-phase chemistry and uptake of gaseous species by particles. In this study, a continuous system, Particle-into-Liquid System (PILS) coupled with two ion chromatographs, was used to obtain PM2.5 ionic chemical composition at a time resolution of 30 min at a suburban site in Hong Kong under three different synoptic conditions. The chemical composition data and meteorological parameters (e.g., temperature, relative humidity (RH)) are input into Aerosol Inorganic Model (AIM-III) for estimation of in-situ pH through calculation of H+ amount and aerosol liquid water content (LWC). The particle pH IS ranged from −1.87 to 3.12, with an average at −0.03, indicating the PM2.5 particles in Hong Kong are highly acidic. Unlike particle strong acidity, which was dominated by sulfate concentration, the amount of aerosol liquid water content could significantly influence in-situ particle acidity. Principal factor analysis has identified the equivalent concentration ratio between cations and anions (i.e., R +/−) and RH to be the two most important factors influencing the particle pH IS. pH IS under different synoptic conditions in this study could be well approximated by a single linear regression equation (slope: 0.95, R 2: 0.93), i.e., pH IS = 4.94 R +/− + 3.11 RH − 5.70. Such an empirical equation provides a convenient mean in estimating particle in-situ acidity for assessing the role of acid-catalyzed aerosol reactions. [Copyright &y& Elsevier]

Abstract: Field observations of atmospheric aerosols have established that organic compounds compose a large fraction of the atmospheric aerosol mass. However, the physical/chemical pathway by which organic compounds are incorporated into atmospheric aerosols remains unclear. The potential role of acid-catalyzed reactions of organic compounds on acidic aerosols has been explored as a possible chemical pathway for the incorporation of organic material into aerosols. In the present study, ultraviolet–visible (UV–vis) spectroscopy was used to monitor the kinetics of formation of the products of the acid-catalyzed aldol condensation reaction of a range of aliphatic aldehydes (C2–C8). The experiments were carried out at various sulfuric acid concentrations and a range of temperatures in order to estimate the rate constants of such reactions on sulfuric acid aerosols under tropospheric conditions. The rate constants were generally found to decrease as the chain length of the aliphatic aldehyde increased (except for acetaldehyde, which had an unusually small rate constant), increase as a function of sulfuric acid concentration as predicted by excess acidity theory, and showed normal Arrhenius behavior as a function of temperature. While the kinetic data are generally consistent with previous laboratory reports of aldehyde reactivity in various sulfuric acid media, the aldol condensation reactions involving aliphatic aldehydes do not appear fast enough to be responsible for significant transfer of organic material into atmospheric aerosols. [Copyright &y& Elsevier]

Mesoporous sulfated Al2O3–ZrO2 (MSAZ) catalysts with large surface areas and pore volumes after calcination at high temperature (650 °C) and with higher Al2O3 content than 20wt% were successfully prepared from a template of block copolymer (P84). The MSAZ catalysts were characterized by X-ray diffraction (XRD), N2 adsorption, transmission electron microscopy (TEM), 27Al magic-angle spinning nuclear magnetic resonance (MAS NMR), thermogravimetric analysis (TG–DTG), temperature-programmed desorption of ammonia (NH3-TPD) and infrared spectra (IR) of adsorbed pyridine. It is shown that the resulting mesostructured sulfated Al2O3–ZrO2 samples have a well-developed textural mesoporosity. The number of acid sites present on MSAZ catalysts is higher than that on conventional sulfated zirconia, and the former catalysts are more active than the latter one for various acid-catalyzed reactions. [ABSTRACT FROM AUTHOR]

Mesoporous sulfated Al2O3–ZrO2 (MSAZ) catalysts with large surface areas and pore volumes after calcination at high temperature (650 °C) and with higher Al2O3 content than 20wt% were successfully prepared from a template of block copolymer (P84). The MSAZ catalysts were characterized by X-ray diffraction (XRD), N2 adsorption, transmission electron microscopy (TEM), 27Al magic-angle spinning nuclear magnetic resonance (MAS NMR), thermogravimetric analysis (TG–DTG), temperature-programmed desorption of ammonia (NH3-TPD) and infrared spectra (IR) of adsorbed pyridine. It is shown that the resulting mesostructured sulfated Al2O3–ZrO2 samples have a well-developed textural mesoporosity. The number of acid sites present on MSAZ catalysts is higher than that on conventional sulfated zirconia, and the former catalysts are more active than the latter one for various acid-catalyzed reactions. [ABSTRACT FROM AUTHOR]

Abstract: While it is well established that organics compose a large fraction of the atmospheric aerosol mass, the mechanisms through which organics are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds with carbonyl groups have recently been suggested as important pathways for transfer of volatile organics into acidic aerosols. In the present study, we use the aerodyne aerosol mass spectrometer (AMS) to probe the uptake of gas-phase hexanal into ammonium sulfate and sulfuric acid aerosols. While both deliquesced and dry non-acidic ammonium sulfate aerosols showed no organic uptake, the acidic aerosols took up substantial amounts of organic material when exposed to hexanal vapor. Further, we used 1H-NMR, Fourier transform infrared (FTIR) spectroscopy and GC–MS to identify the products of the acid-catalyzed reaction of hexanal in acidic aerosols. Both aldol condensation and hemiacetal products were identified, with the dominant reaction products dependent upon the initial acid concentration of the aerosol. The aldol condensation product was formed only at initial concentrations of 75–96wt% sulfuric acid in water. The hemiacetal was produced at all sulfuric acid concentrations studied, 30–96wt% sulfuric acid in water. Aerosols up to 88.4wt% organic/11.1wt% H2SO4/0.5wt% water were produced via these two dimerization reaction pathways. The UV-VIS spectrum of the isolated aldol condensation product, 2-butyl 2-octenal, extends into the visible region, suggesting these reactions may impact aerosol optical properties as well as aerosol composition. In contrast to previous suggestions, no polymerization of hexanal or its products was observed at any sulfuric acid concentration studied, from 30 to 96wt% in water. [Copyright &y& Elsevier]

Abstract: Recent observations in ambient PM2.5 of 2-methylthreitol, 2-methylerythritol and 2-methylglyceric acid, proposed isoprene oxidation products, suggest the contribution of isoprene to SOA formation, long thought to be relatively unimportant, should be reexamined. To address this issue, an isoprene/NO X /air mixture was irradiated in a flow reactor smog chamber in both the absence and presence of SO2 to measure the SOA yield of isoprene and to establish whether the two 2-methyl tetrols and 2-methylglyceric acid are present in isoprene SOA and could serve as SOA indicator compounds. In the absence of SO2, the SOA yield of 0.002 was low, as expected, although uncertain because the SOA concentration was near chamber background levels. However, in the presence of SO2, the SOA yield increased significantly to 0.028. Analysis of the trimethylsilyl derivatives of the SOA samples by gas chromatography/mass spectrometry showed chamber concentrations of the two 2-methyl tetrols totaling 0.1μgm−3 and a 2-methylglyceric acid concentration of 0.4μgm−3 in the absence of SO2, with the levels increasing significantly to 6.3μgm−3 and 1.2μgm−3, respectively, when SO2 was added. The laboratory data suggest that these compounds are possible indicator compounds for isoprene SOA and that the presence of SO2 enhances significantly SOA formation from isoprene photooxidation, with acid-catalyzed reactions possibly playing a major role. The importance of these findings was supported by the detection of the two 2-methyl tetrols and 2-methylglyceric acid in summertime ambient PM2.5 samples collected at three locations in the eastern United States. However, additional mechanistic studies are required to predict the contributions of the SO2-assisted isoprene SOA formation to ambient PM2.5 concentrations. [Copyright &y& Elsevier]

The catalytic potential of catalysts for acid-catalyzed reactions has been demonstrated by NaY zeolite loaded with alkylsilane-covered niobic acid in the liquid phase hydration of 1,2-epoxyoctane with water. The catalytic activity of the catalysts was correlated to the amphiphilic character of the solid catalyst particles. [ABSTRACT FROM AUTHOR]

ZSM-12 and several other 12-membered ring large-pore zeolites have been tested for the reforming of naphthenic hydrocarbon mixtures. It was found that ZSM-12 possesses a surprisingly higher coking resistance than other large pore zeolites tested such as USY, L-zeolite, mordenite, and β=zeolite for reforming of hydrocarbon mixtures. This superior performance is due to the unique non-interconnecting tubular-like linear channels of ZSM-12, which do not allow trapping/accumulation of coking precursors. ZSM-12 zeolite also demonstrated excellent structural stability even under severe acid dealumination. From this work, we found that the decrease of the aluminum content of a zeolite is not sufficient to ensure low rates of coke deposition. We also concluded that zeolites with channel intersections (cavities) of comparable size with the zeolite apertures do not favor coke formation. For these types of zeolites the strong acid sites carry out other acid-catalyzed reactions, rather than forming coke. In contrast, zeolites with relatively large supercages are inherently favorable to coking reactions, which in turn lead to the fast deactivation. The appropriate combination of the zeolite pore structure and acidity (controlled via dealumination) showed superior TOS behavior (time-stable activity and product selectivities). For zeolites which are susceptible to coking due to pore structure, the increase of the Brønsted acid strength results in fast deactivation. Contrary to what one would commonly expect and previous reports, we found that one-dimensional zeolites, such as, ZSM-12, can exhibit significantly higher tolerance to coking than multidirectional zeolites. [ABSTRACT FROM AUTHOR]

Supported WO x clusters are active and stable catalysts for isomerization, dehydration, and cracking reactions. Brønsted acid sites form on WO x clusters when a lower valent element replaces W6 + or when W6 + centers reduce slightly during catalytic reactions. WO x clusters of intermediate size provide the balance between reducibility and accessibility required to maximize the number of surface H+ species in WO x–ZrO2, zirconium tungstate, and oxygen-modified WC catalysts. H2 is involved in the generation and maintenance of Brønsted acid sites during catalytic reactions on WO x clusters. [ABSTRACT FROM AUTHOR]

The solution-phase stability of the hydronium ion catalyst significantly affects the rates of acid-catalyzed reactions, which are ubiquitously utilized to convert biomass to valuable chemicals. In this work, classical molecular dynamics simulations were performed to quantify the stability of hydronium and chloride ions by measuring their solvation free energies in water, 1,4-dioxane (DIOX), tetrahydrofuran (THF), γ-valerolactone (GVL), N-methyl-2-pyrrolidone (NMP), acetone (ACE), and dimethyl sulfoxide (DMSO). By measuring the free energy for transferring a hydronium ion from pure water to pure organic solvent, we found that the hydronium ion is destabilized in DIOX, THF, and GVL and stabilized in NMP, ACE, and DMSO relative to water. The distinction between these organic solvents can be used to predict the preference of the hydronium ion for specific regions in aqueous mixtures of organic solvents. We then incorporated the stability of the hydronium ion into a correlative model for the acid-catalyzed conversion of 1,2-propanediol to propanal. The revised model is able to predict experimental reaction rates across solvent systems with different organic solvents. These results demonstrate the ability of classical molecular dynamics simulations to screen solvent systems for improved acid-catalyzed reaction performance.