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Developing an earth-abundant catalyst that is sulfur-tolerant, active, and highly selective is of great interest for valorizing natural gas streams containing sour gas. A tin-modified alumina catal...

Summary Calcium hydroxyapatite (HAp) has emerged as a green, bifunctional catalyst for the heterogeneous coupling of various biomass-derived molecules, including ethanol to n-butanol via the Guerbet reaction. This review critically analyzes the surface chemistry of HAp catalysts based on the available temporally- and spatially-resolved in situ and operando spectroscopic studies. Specifically, the nature of the isolated acidic and basic surface sites, as well as the acid-base pairs, is elucidated based on chemical probe spectroscopy results. Surface structure-reactivity relationships are also rationalized based on the nature and identity of the surface sites involved in various steps of the Guerbet reaction to produce n-butanol over the HAp catalysts. Finally, future directions in experimental investigations are suggested to guide the rational design of improved HAp-based catalysts for the Guerbet reaction and other similar chemistries.

The complex structure of the catalytic active phase, and surface-gas reaction networks have hindered understanding of the oxidative coupling of methane (OCM) reaction mechanism by supported Na 2 WO 4 /SiO 2 catalysts. The present study demonstrates, with the aid of in-situ Raman and chemical probe (H 2 -TPR, TAP and steady-state kinetics) experiments, that the long speculated crystalline Na 2 WO 4 active phase is unstable and melts under OCM reaction conditions, partially transforming to thermally stable dispersed surface Na-WO x sites. Kinetic analysis via temporal analysis of products (TAP) and steady-state OCM reaction studies demonstrate that ( i ) surface Na-WO x sites are responsible for selectively activating CH 4 to C 2 H x and over-oxidizing CH y to CO and ( ii ) molten Na 2 WO 4 phase is mainly responsible for over-oxidation of CH 4 to CO 2 and also assists in oxidative dehydrogenation of C 2 H 6 to C 2 H 4 . These new insights reveal the nature of catalytic active sites and resolve the OCM reaction mechanism over supported Na 2 WO 4 /SiO 2 catalysts.

Catalytic dimerization of ethylene (C2H4) to butene (C4H8) utilizes homogenous catalysts composed of transition metal molecular complexes in the presence of a co-catalyst or Ni, Rh or Cr supported heterogeneous catalysts. Recently, a heterogeneous cobalt catalyst supported on NH4OH-treated carbon (Co/N C) has gained attention. However, the structure of the active site, the identity of the active phase, the role of NH4OH treatment and the effect of thermal activation have remained elusive. Herein, in situ Raman spectroscopy showed the absence of crystalline cobalt oxide phases, such as CoO or Co3O4, in the working catalyst. An intense Raman band at 810 cm−1 was detected in the as-synthesized catalyst, which corresponds to μCo-peroxo species formed via auto-oxidation of the [Co(NH3)x]2+ sites during the drying step. UV–vis DRS absorbance bands at ∼286, 340 and 560 nm indicated that a mixture of octahedral Co3+ and Co2+ is present in the as-synthesized catalyst. During thermal treatment in inert atmosphere, the 265 and 810 cm−1 Raman bands diminished signifying the reduction of μCo-peroxo sites, with the oxidation of some NH3 ligands to N2O(g), indicated by an IR doublet at ∼2225 cm−1. UV–vis DRS during thermal treatment corroborated the reduction of Co3+ to Co2+, with Co2+ sites coordinated in a tetrahedral fashion, as indicated by a new absorbance band at ∼600−700 nm. The presence of the immobilized pseudo-tetrahedral [Co(NH3)x]2+ molecular complexes active for dimerization is proposed as an alternative to previous reports that attribute olefin dimerization activity to crystalline cobalt oxide phase in this catalyst. Steady-state catalytic test results at 1 bar, 80 °C, 5.0 % C2H4 at 10 sccm, 0.3 g catalyst show that model catalyst containing crystalline cobalt oxides (Co/C) exhibited similar initial butene productivity to the [Co(NH3)x]2+ containing Co/N C catalyst, but suffered sharper deactivation due to the irreversible olefin deposition on Co3+ sites.

Oxidative dehydrogenation of propane to propylene can be achieved using conventional, oxygen-assisted dehydrogenation of propane (O2–ODHP) or via the use of soft oxidants, such as CO2, N2O, S-conta...

A bulk γ-Al2O3 catalyst shows high selectivity for propane dehydrogenation upon pretreatment and co-feeding with H2S. The reaction kinetics, deactivation rates, and active sites for propane dehydrogenation on this catalyst were characterized using fixed bed conversion studies, NH3-TPD, O2-TPO, XPS, and density functional theory (DFT). Specifically, we observe that the selectivity to propylene was 94% at ca. 16% propane conversion at 560 °C for a C3H8:H2:H2S ratio of 1.1:1:0.1 on γ-Al2O3. Our results indicate that H2S can irreversibly modify the active sites of γ-Al2O3, postulated to be defect sites on the 110 facet comprised of a tri-coordinated Al atom, such that the modified site was more active and selective towards propylene and less inhibited by co-fed H2S. Along with XPS and O2-TPO, the dehydrogenation-regeneration experiments suggest the formation of sulfurous coke and strong adsorption of reaction products result in a less active catalyst. This study shows the potential of alumina/metal-sulfide as an earth-abundant and relatively benign class of catalysts for alkane activation, especially in the context of sour natural gas upgrading.

The experimentally validated computational models developed herein, for the first time, show that Mn-promotion does not enhance the activity of the surface Na2WO4 catalytic active sites for CH4 heterolytic dissociation during OCM. Contrary to previous understanding, it is demonstrated that Mn-promotion poisons the surface WO4 catalytic active sites resulting in surface WO5 sites with retarded kinetics for C–H scission. On the other hand, dimeric Mn2O5 surface sites, identified and studied via ab initio molecular dynamics and thermodynamics, were found to be more efficient in activating CH4 than the poisoned surface WO5 sites or the original WO4 sites. However, the surface reaction intermediates formed from CH4 activation over the Mn2O5 surface sites are more stable than those formed over the Na2WO4 surface sites. The higher stability of the surface intermediates makes their desorption unfavorable, increasing the likelihood of over-oxidation to COx, in agreement with the experimental findings in the literature on Mn-promoted catalysts. Consequently, the Mn-promoter does not appear to have an essential positive role in synergistically tuning the structure of the Na2WO4 surface sites towards CH4 activation but can yield MnOx surface sites that activate CH4 faster than Na2WO4 surface sites, but unselectively., The experimentally validated computational models developed herein, for the first time, show that Mn-promotion does not necessarily enhance the activity of the surface Na2WO4 catalytic active sites for CH4 heterolytic dissociation during OCM.

This review focuses on recent fundamental insights about methane dehydroaromatization (MDA) to benzene over ZSM-5-supported transition metal oxide-based catalysts (MOx/ZSM-5, where M = V, Cr, Mo, W, Re, Fe). Benzene is an important organic intermediate, used for the synthesis of chemicals like ethylbenzene, cumene, cyclohexane, nitrobenzene and alkylbenzene. Current production of benzene is primarily from crude oil processing, but due to the abundant availability of natural gas, there is much recent interest in developing direct processes to convert CH4 to liquid chemicals. Among the various gas-to-liquid methods, the thermodynamically-limited Methane DehydroAromatization (MDA) to benzene under non-oxidative conditions appears very promising as it circumvents deep oxidation of CH4 to CO2 and does not require the use of a co-reactant. The findings from the MDA catalysis literature is critically analyzed with emphasis on in situ and operando spectroscopic characterization to understand the molecular level details regarding the catalytic sites before and during the MDA reaction. Specifically, this review discusses the anchoring sites of the supported MOx species on the ZSM-5 support, molecular structures of the initial dispersed surface MOx sites, nature of the active sites during MDA, reaction mechanisms, rate-determining step, kinetics and catalyst activity of the MDA reaction. Finally, suggestions are given regarding future experimental investigations to fill the information gaps currently found in the literature.

Kinetic modeling of single-step catalytic conversion of ethanol to 1,3-butadiene is necessary to inform accurate process design. This paper uses first-principles-informed energy span and microkinetic analysis to explore the reaction free energy landscapes and kinetic limitations of competing reaction pathways on a MgO (100) step-edge. Previous studies suggested mechanisms proceeding via both dehydrogenation and dehydration of ethanol, and highlighted sensitivity to conditions and catalyst composition. Here, we use the energy span concept to characterize the theoretical maximum turnover and degree of turnover frequency control for states in each reaction pathway, finding the dehydration route to be less active for 1,3-butadiene, and suggesting rate-determining states in the dehydrogenation, dehydration, and condensation steps. The influence of temperature on the relative rate contribution of each state is quantified and explained through the varying temperature sensitivity of the free energy landscape. A microkinetic model is developed to explore competition between pathways, interaction with gas-phase species, and surface coverage limitations. This suggests that the turnover may be significantly lower than predicted solely based on energetics. Turnover frequency determining states found to have high surface coverage include adsorbed ethanol and two longer, oxygenated hydrocarbons. The combined energy span and microkinetic analysis permits investigation of a complex system from two perspectives and helps elucidate conflicting observations of rate determining steps and product distribution by considering both energetic and kinetic limitations. The impact of uncertainty in the energy landscape is quantified using a correlated error model. While the range of predictions is large, the average performance and trends are similar.

The nature of isolated tungsten oxide (WOx) sites in the dispersed phase on the surface of a β-cristobalite (β-SiO2) support in undoped and Na- or Mn-doped WOx/SiO2 model catalysts used for the oxi...

The molecular and electronic structures and chemical properties of the active sites on the surface of supported Na2WO4/SiO2 catalysts used for oxidative coupling of methane (OCM) are poorly understood. Model SiO2-supported, Na-promoted tungsten oxide catalysts (Na–WOx/SiO2) were systematically prepared using various Na- and W-precursors using carefully controlled Na/W molar ratios and examined with in situ Raman, UV-vis DR, CO2-TPD-DRIFT and NH3-TPD-DRIFT spectroscopies. The traditionally-prepared catalysts corresponding to 5% Na2WO4 nominal loading, with Na/W molar ratio of 2, were synthesized from the aqueous Na2WO4·2H2O precursor. After calcination at 800 °C, the initially amorphous SiO2 support crystallized to the cristobalite phase and the supported sodium tungstate phase consisted of both crystalline Na2WO4 nanoparticles (Na/W = 2) and dispersed phase Na–WO4 surface sites (Na/W < 2). On the other hand, the catalysts prepared via a modified impregnation method using individual precursors of NaOH + AMT, such that the Na/W molar ratio remained well below 2, resulted in: (i) SiO2 remaining amorphous (ii) only dispersed phase Na–WO4 surface sites. The dispersed Na–WO4 surface sites were isolated, more geometrically distorted, less basic in nature, and more reducible than the crystalline Na2WO4 nanoparticles. The CH4 + O2-TPSR results reveal that the isolated, dispersed phase Na–WO4surface sites were significantly more C2selective, but slightly less active than the traditionally-prepared catalysts that contain crystalline Na2WO4 nanoparticles (Na/W = 2). These findings demonstrate that the isolated, dispersed phase Na–WO4 sites on the SiO2 support surface are the selective-active sites for the OCM reaction.

Natural gas is often sour, containing varying amounts of H2S and CO2. Gas sweetening processes that are routinely used rely on processes such as amine-based adsorption–desorption cycles, membrane s...

The literature for the oxidative coupling of methane (OCM) on supported Mn/Na2WO4/SiO2 catalysts is systematically and critically reviewed. The influence of the precursors, starting SiO2 support cr...

This article critically reviews the literature on sulfated zirconia catalysts for variety of important hydrocarbon and oxygenate reactions including ethylene dimerization, isomerization, alkylation and esterification. The catalyst synthesis method-resulting molecular structure relationships, stability and reactive transformations of the active site in response to gas phase environment, reaction mechanisms, reaction intermediates, the corresponding kinetics and effect of some popular promoters are covered. Key structural features of the active sites have been extensively investigated but the conclusive structure is yet to be determined due to the diversity of the preparation methods (nature and crystallinity of the support, sulfate deposition method, sulfate coverage) as well as the diversity of the experimental conditions used during the spectroscopic determination. Similarly, the effect of the promoters and the synergistic effects of the promoter/sulfate sites in the presence of hydrocarbons are not well-defined. Finally, multiple theories exist for the reactive mechanisms on sulfated zirconia but most rely on the homogeneous reaction mechanisms, such as those for ethylene dimerization and butane alkylation with butane. Collectively, these show the lack of a fundamental understanding and the need of modern catalysis studies of this important catalytic system.

Salt cocrystals with components that assemble by hydrogen bonds and aromatic anion-molecule stacks (π--π stacks) are reported. U-shaped bipyridines and an isocoumarin carboxylic acid self-assemble to form 5-, 6-, and 10-component aggregates with components in double and quadruple face-to-face stacks. DFT calculations support the π--π stacks to help stabilize the salt cocrystals.

A large fraction of the global natural gas reserves is in the form of sour gas, i.e. contains hydrogen sulfide (H2S) and carbon dioxide (CO2), and needs to be sweetened before utilization. The traditional amine-based separation process is energy-intensive, thereby lowering the value of the sour gas. Thus, there is a need to find alternative processes to remove, e.g., hydrogen sulfide. Mo6S8 clusters are promising candidates for transforming methane (CH4) and hydrogen sulfide into methanethiol (CH3SH) and dimethyl sulfide (CH3SCH3), which are high-value sulfur-containing products that can be further used in the chemical industry. Here first-principles microkinetics is used to investigate the activity and selectivity of bare and promoted (K, Ni, Cl) Mo6S8. The results show that methanethiol is produced via two different pathways (direct and stepwise), while dimethyl sulfide is formed via a competing pathway in the stepwise formation of methanethiol. Moreover, there is an increase in activity and a decrease in selectivity when adding an electropositive promoter (K), whereas the reverse behaviour is observed when adding an electronegative promoter (Cl). When adding Ni there is also a decrease in activity and an increase in selectivity; however, Ni is acting as an electron donor. The results provide insights and guidance as to what catalyst formulation is preferred for the removal of hydrogen sulfide in sour gas.

The electronic structure and reactivity of Cu- and Zn-promoted wet-kneaded MgO/SiO2 catalysts was interrogated during ethanol reaction to 1,3-BD. A multimodal nature of characterization, including in situ or operando X-ray, electron, light spectroscopies, and steady state reactivity measurements demonstrated critical information on the temporal evolution of the catalyst active sites including key measurements performed in operando conditions using synchrotron techniques (EXAFS and XANES). In situ DRIFT spectroscopy allowed decoupling of the aldol condensation and dehydrogenation reactive steps due to the promotion with enhanced ability to carry out aldol condensation, as correlated with the steady state reactivity experiments. In situ UV–vis spectroscopy presented a complex picture of the adsorbates with π–π* electronic transitions due to the allylic cations, cyclic or aromatic species while also suggesting oligomeric CuO species were formed. Operando X-ray measurements combined with ab initio multiple sc...

Molecular structures of the unpromoted and K2O-promoted supported WO3/Al2O3 catalysts were studied with in situ Raman and UV–vis spectroscopy. In situ Raman spectra revealed that supported 20% WO3/Al2O3 corresponds to near monolayer coverage of isolated and oligomeric surface WOx species on Al2O3. Above monolayer surface WOx coverage (21% WO3/Al2O3), crystalline WO3 nanoparticles are also present. The addition of K2O to the supported WO3/Al2O3 catalyst increased the concentration of isolated surface WOx species and did not form K2WO4 nanoparticles. The reducibility of the tungsten oxide structures depends on their structures (2D or 3D) and the K2O promoter. Their interaction with acidic CO2 and SO2 gases was also investigated. Adsorption of CO2 creates several surface carbonate species of varying acidity that were detected using a combination of in situ IR and mass spectroscopy. Adsorbed bicarbonate form on weakly basic surface sites on tungsten oxide monolayer WO3/Al2O3 catalyst as well as in the presence of low 2.5% K2O loading. At high 5% K2O loading, the presence of the strong surface basic sites yields adsorbed carbonates. After SO2 pretreatment, however, new strongly adsorbed sulfate appears on the surface that inhibits CO2 adsorption.

Ethanol is an important renewable chemical that allows for sustainable high-value product, such as 1,3-butadiene, catalytic synthesis. The MgO/SiO2 catalyst is typically utilized in a single-step ethanol-to-1,3-butadiene catalytic conversion, and the (by)product yields were shown to depend on the type, structure, and strength of the catalytic active sites. The fundamental factors describing the molecular structure and binding properties of these sites are thus of critical importance but not yet fully understood. We utilized a multimodal approach, including temperature-programmed surface-sensitive infrared mass spectrometry using probe molecules, such as CO2, NH3, and pyridine and propionic acids, to unravel the structure and persistence of these catalytic sites in situ. In particular, Mg–O–Mg, Mg–O(H)–Mg, Mg–O–Si, and Mg–O(H)–Si surface site binding configurations were proposed and scrutinized using spectroscopic methods in combination with density functional theory (DFT) calculations. A combination of NH...

Incipient wetness impregnation was used to deposit dispersed tin (Sn) atoms on γ-Al2O3. The morphology and structure of the catalysts were characterized using Raman, X-ray Photoelectron Spectroscopy (XPS), and low energy ion scattering (LEIS) combined with N2-physisorption and in situ infrared diffuse reflectance spectroscopy (DRIFTS) using NH3 and CO2 as probe molecules, H2- temperature-programmed reduction (H­2-TPR), and steady-state reaction kinetics measurements. The effects of H2S on the surface chemical composition and structure of the resulting catalysts were systematically studied. The results showed isolated and well-dispersed Sn oxide sites of the deposited catalyst with nanoparticles observed only at relatively high coverages of 10% Sn at a coverage ranging from 0.48 to 2.8 Sn atoms nm−2. DRIFT spectroscopy evidenced a decrease in the number of Lewis acid sites on H2S treated Sn/Al2O3 suggesting surface tin species re-dispersing and blocking the active sites of γ-Al2O3. Overall, the surface analysis results presented here suggest that the active catalytic sites in the presence of H2S involve Al2O3 rather than bulk sulfide and Sn atoms dispersed over alumina towards propane dehydrogenation.

A complete separation scheme has been designed for the effluent of a high-pressure ethanol-to-butanol catalytic reactor, producing 250,000 tonnes of n-butanol per year. The effluent contains water, hydrogen and a diverse range of C2-C4 oxygenates: unconverted ethanol, n-butanol, acetaldehyde, ethyl acetate, and acetal. Fundamental phase equilibrium relationships suggested use of conventional, extractive, and heterogeneous azeotropic distillation units to perform the separations. All reactor effluent species exit the separation process at mole purities of at least 99%. Separation costs are estimated to range from 9.0 to 10.6 MJ/kg n-butanol, which is comparable with the separation costs of n-butanol obtained from established acetone-butanol-ethanol (ABE) separation process.

Mesoporous Fe-doped MgO nanoparticles were synthesized using a facile sol-gel method and utilized for photo-Fenton-like degradation of salicylic acid (SA). The MgO surface dissolution facilitated an increase in the pH under the reaction conditions that allowed the Fe-MgO catalyst to be active without detectable iron leaching. Under simulated solar radiation, SA was completely degraded with an initial rate constant of 0.048 min−1 at the optimal reaction conditions of 500 ppm loading of 5% Fe-MgO, 20 mM H2O2 concentration, and 50 ppm SA concentration. The catalyst was stable over 5 reaction cycles. The Fe-MgO catalyst was shown to have a surface area up to 171 m2/g and contain hematite (Fe2O3) nanoparticles with octahedrally coordinated iron catalytic centers, as inferred from diffuse reflectance UV–vis measurements. Post-reaction catalyst characterization showed that some Fe2+ was present in the catalyst due to the redox cycle during the chain initiation and propagation steps of the reaction.

In this work, we performed periodic Density Functional Theory calculations and explored reactive pathways of ethanol catalysis to catalytically form 1,3-butadiene on undoped MgO surface. We have identified critical reactive intermediates, as well as thermodynamic and kinetic barriers involved in the overall reactive landscape. The overall free energy surface was explored for the highly debated reaction mechanisms, including Toussaint’s aldol condensation mechanism, Fripiat’s Prins mechanism and mechanism based on Ostromislensky’s hemiacetal rearrangement. Thermodynamics and kinetics data calculated showed four rate limiting steps in the overall process. In particular, ethanol dehydration to form ethylene possessed lower energy barrier than dehydrogenation to yield acetaldehyde suggesting competing reactive pathways. C C bond coupling to form acetaldol (3-hydroxybutanal) is preceded with 16 kcal/mol forward reaction barrier. Direct reaction of ethylene and acetaldehyde proceeds with a free energy barrier of 29 kcal/mol suggesting that Prins condensation is an alternative route. Finally, thermodynamic stability of 1-ethoxyethanol prevents further reaction via hemiacetal rearrangement. The results here provide a first glimpse into the overall 1,3-butadiene formation mechanism on undoped MgO reactive sites in light of the vast literature discussing variety of the proposed mechanistic pathways mostly based on conventional homogenous organic chemistry reactions.

The abundance of natural gas reserves can facilitate the transition from fossil derived to fully renewable chemical and fuel generation. Natural gas, however, can contain more than 10% sour gas molecules (chiefly CO2 and H2S), especially in the Middle East and Russia. Currently, the most common sour natural gas separation technologies rely on the use of various amine-based absorption–desorption cycles in absorption towers, membrane separation and cryogenic processes. However, these processes are quite expensive and, unfortunately, result in the necessity for further processing of the sour gas stream. We feel that the implementation of catalytic activation of the sour gas stream, so as to form useful products, has been underexplored and thus has yet to be fully developed. In this paper, we present a series of catalytic reactions for the sour gas components so as to obtain useful chemicals or fuels, such as carbon disulfide (CS2), hydrogen (H2), ethylene (C2H4), ammonium sulfate ((NH4)2SO4) and ammonium thiosulfate ((NH4)2S2O3). Particular catalytic reactions which can form those products are (a) CH4 reforming with H2S on supported metal oxide catalysts, (b) CO2 + H2S + H2 catalytic reaction on K2O/WO3/Al2O3 to yield a CH3SH intermediate, (c) olefin production via CH3SH coupling on zeolites and supported metal oxides and (d) H2S + NH3 catalytic reaction to yield ammonium sulfate ((NH4)2SO4) and ammonium thiosulfate ((NH4)2S2O3) on partial oxidation catalysts. Thermodynamic considerations, together with catalyst design techniques, are discussed for each reaction.

Direct processing of sour, e.g. containing large amounts of acidic H2S and/or CO2 molecules, natural gas is of direct interest as vast amounts of it are available and accessible but are underutilized. While sour natural gas is still treated using energy-intensive amine absorption/desorption, here we propose and describe a first step in catalytically producing a value added chemical and energy carrier, CH3SH and H-2, respectively. For this purpose, we performed Density Functional Theory (DFT) and microkinetic modelling of CH4 and H2S reaction pathways to form CH3SH and H-2 as a first step in elucidating complex yet not explored pathways in oxygen-free sour gas reforming. For this purpose, we utilized bare unpromoted and K-or Nipromoted Mo6S8 clusters. CH4 dissociation was found to be the rate-determining step above 1100 K on Ni-promoted Mo6S8 while H-2 formation was the rate-determining step on the bare and K-promoted Mo6S8. At lower reaction temperatures between 800 and 1100 K, CH3SH formation becomes an important step, especially on Ni-Mo6S8. This method presents an interesting route of direct catalytic sour natural gas processing which potentially leads to high-value hydrocarbons, such as ethylene, using CH3SH as a reactive intermediate.

1,3-Butadiene is an important commodity chemical and new, selective routes of catalytic synthesis using green feedstocks, such as ethanol, is of interest. For this purpose, surface chemistry of MgO/SiO2 catalyst synthesized using wet-kneading was explored during the reaction of ethanol and the corresponding reactive intermediates, including acetaldehyde, crotonaldehyde, crotyl alcohol using temperature programmed in situ DRIFT spectroscopy combined with DFT calculations. Ethanol adsorption yielded several physisorbed and chemisorbed surface species. Acetaldehyde exhibited high reactivity to form crotonaldehyde. However, aldehyde intermediates resulted in strongly bound surface species stable even at high temperatures, assigned to surface acetate, and/or 2,4-hexadienal or polymerized acetaldehyde. Crotonaldehyde was reduced by ethanol to yield crotyl alcohol via MPV mechanism. Crotyl alcohol, on the other hand, showed to be very reactive and yield two different species on the surface, namely physisorbed and deprotonated that would further desorb as 1,3-BD. Presence of gas phase hydrogen containing molecules, such as ethanol, proved to be key in several reactive steps, including acetaldehyde condensation step and crotonaldehyde reduction. Altogether, these data suggested complex reactive interactions between the surface hydroxyl groups, gaseous reactants and surface bound reactive intermediates during the 1,3-BD formation. Future work is needed to correlate vapor phase product evolution with the transient reactive surface intermediates to examine trends leading to higher overall 1,3-BD selectivity.

Natural gas is envisioned as a primary source of energy and hydrocarbons in the foreseeable future. Though shale gas has recently become abundant, it has two main concerns: its environmental impact and sustainable utilization. The former is the result of recent reports of natural gas emissions and flares into the environment, where it acts as a powerful greenhouse gas, whereas the latter is dictated by the need for efficient hydrocarbon utilization. Modern natural gas processing units that yield clean fuels and feedstock from methane, CH 4 , require extremely large capital investments and are not economical in remote natural gas extraction sites. Single step (direct), non-syngas based catalytic routes of CH 4 conversion to value added products have not been competitive economically and need to be reevaluated in the light of shale gas availability. This perspective discusses general considerations for the desired hydrocarbon products, the thermodynamic limitations involved in a single step conversion of CH 4 and heterogeneous catalytic routes based on high temperatures and oxide based catalysts. We then discuss other catalysts and methods of CH 4 activation that have recently emerged and are conceptually different from metal oxide catalyst based routes, such as those using sulfur or halogens. Lastly, we discuss a possible route of CH 4 monetization beyond the first reactive product (such as ethylene oligomerization into fuels), as well as currently explored photo(electro)chemical routes of CH 4 activation.

Lignocellulos biomass can be converted to bio-oil containing aliphatic hydrocarbons via catalytic pyrolysis at 500 °C in the presence of Cs modified amorphous silica alumina (Cs/ASA). The reaction routes for the formation of aliphatic hydrocarbons was studied using biomass constituent, viz. cellulose, hemicellulose, lignin, and single model components in a pyrolyzer system in conjunction with GC/MS. The pyrolysis behaviour of each biomass constituent was also studied using TGA. The results showed that in the presence of Cs/ASA catalyst aliphatic hydrocarbons can be formed from all the three constituents but mainly from lignin (35% of total peak area compared to 10% for cellulose) resulting in high quality bio-oil with 40 Mj kg −1 heating value. On the other hand, the pyrolysis of single model compounds did not result in the aliphatic hydrocarbons. However, pyrolysis of mixture of the model compounds yielded in aliphatic hydrocarbons indicating effect of intermolecular interactions such as hydrogen transfer over Cs + ions.

Al2O3-supported tungsten oxide catalysts have been instrumental in many industrially relevant reactions and their reactivity is controlled by their molecular structure. In turn, their molecular structure has primarily been derived via Raman measurements with assignments made using model compounds of known local (molecular) coordination. In this work, the structure and simulated Raman spectra of unpromoted and K+-promoted tungsten oxide catalyst monomeric sites supported on γ-Al2O3(110) (K2O/WOx/γ-Al2O3(110)) were studied using periodic DFT methods. Two different WOx-grafted monomers on the γ-Al2O3(110) surface were identified with a total energy difference of 0.17 eV between both structures. Importantly, both structures showed the presence of W=O and W-OH moieties, thus providing additional insights into experimental Raman data, which typically describe only W=O moieties. The grafted WO3 species were stabilized when the present W-OH groups were oriented toward the alumina surface leading to the formation of H-bonds, calculated at 1039 cm-1, for example in the vicinity of the W=O vibrations. The W=O bond length was altered in the presence of K+, as shown experimentally and theoretically in blue shifting of the Raman band corresponding to W=O. The W vibrations were well localized in the calculated spectra, and little shifts were observed upon the different WOx molecular geometry, explaining why a single Raman peak is mostly observed experimentally. The acidity of the lowest energy catalyst structures was investigated by simulated NH3 adsorption vibrational frequency and binding energy calculations. Results suggested that NH3 prefers to bind in a Lewis-like structure with no proton donation from either W-OH or Al-OH moiety. This challenged some of the literature observations where Brønsted acid sites have been suggested to exist on near-monolayer coverage WOx species on γ-Al2O3 prepared by calcining at moderate (400 °C) to high temperatures (700 °C). Overall, this work provided new insights into the molecular structure of WOx/γ-Al2O3 and K2O/WOx/γ-Al2O3 catalysts not immediately available from experimental measurements alone. Fil: Kiani, Daniyal. Lehigh University; Estados Unidos Fil: Belletti, Gustavo Daniel. Universidad Nacional del Litoral. Instituto de Química Aplicada del Litoral. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Química Aplicada del Litoral.; Argentina Fil: Quaino, Paola Monica. Universidad Nacional del Litoral. Instituto de Química Aplicada del Litoral. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Química Aplicada del Litoral.; Argentina Fil: Tielens, Frederik. Vrije Unviversiteit Brussel; Bélgica Fil: Baltrusaitis, Jonas. Lehigh University; Estados Unidos

Glycerol exists in large amounts owing to its role as a byproduct in biodiesel production, and thanks to its chemical composition, it can be converted into more high-value products, such as mono- and polyethers, esters, diols, acrolein, and others. Hence, predicting glycerol-reactive properties is of utmost importance for designing efficient catalytic processes for its selective (electro)catalytic transformations; however, such an understanding is still far from complete. In this work, we performed quantum chemical calculations to validate a range of dispersion-corrected functionals to accurately predict and interpret structural, electronic, and vibrational properties of glycerol adsorbed on bare and transition-metal surface-alloyed Au(111) surface. optB86b-vdW (van der Waals) was found to have the overall best agreement with experiments concerning lattice constant, bulk stress, surface energy, and methanol adsorption among PBE (Perdew–Burke–Ernzerhof), optB88-vdW, optPBE-vdW, vdW-DF (density functional),...

A smart ionic co-crystal of urea with KCl and ZnCl2 has been obtained in two polymorphic modifications via mechanochemical and solution methods and proven to be a very efficient urease inhibitor while, simultaneously, able to provide soil nutrients to complement N supply.

The photocatalytic decomposition of cortisone 21-acetate (CA), a model compound for the commonly used steroid, cortisone, was studied. CA was photocatalytically decomposed in a slurry reactor with the initial rates between 0.11 and 0.46 mg L(-1)min(-1) at 10 mg L(-1) concentration, using the following heterogeneous photocatalysts in decreasing order of their catalytic activity: ZnOEvonik TiO2 P25Hombikat TiO2WO3. Due to the lack of ZnO stability in aqueous solutions, TiO2 P25 was chosen for further experiments. The decomposition reaction was found to be pseudo-first order and the rate constant decreased as a function of increasing initial CA concentration. Changing the initial pH of the CA solution did not affect the reaction rate significantly. The decomposition reaction in the presence of the oxidizing sacrificial agent sodium persulfate showed an observed decomposition rate constant of 0.004 min(-1), lower than that obtained for TiO2 P25 (0.040 min(-1)). The highest photocatalytic degradation rate constant was obtained combining both TiO2 P25 and S2O8(2-) (0.071 min(-1)) showing a synergistic effect. No reactive intermediates were detected using LC-MS showing fast photocatalytic decomposition kinetics of CA.

We present a novel high throughput photocatalyst efficiency assessment method based on 96-well microplates and UV-Vis spectroscopy. We demonstrate the reproducibility of the method using methyl orange (MO) decomposition, and compare kinetic data obtained with those provided in the literature for large conventional photoreactors. To demonstrate the example of the method capabilities, we rapidly screened the effects of salts, potentially present in wastewater, on kinetic rates of MO decomposition, and briefly discuss the obtained data comparing it with the existing literature obtained using conventional photoreactors.

Several remarkable observations regarding structure, (surface) composition and visible light induced photocatalytic activity of Bi-promoted Anatase photocatalysts are reported. First, XPS characterization data show that compositions of mixed Bi-Ti-oxide phases obtained by hydrothermal treatment at 180 °C of aqueous solutions of ethanol, titanium n-butoxide, and bismuth nitrate, are surface enriched with a specific fraction of metallic-like bismuth. Second, the formation of highly dispersed nanoparticles of platinum on these composites by photo-deposition is accompanied by significant morphological changes. Third, the platinum functionalized, bismuth-promoted Anatase composites exhibit extraordinary photocatalytic activity in the photocatalytic degradation of organic compounds (acid orange 7 and salicylic acid, respectively) upon illumination at 447 nm, higher than observed for P25 upon UV illumination in similar reactor configuration. An optimized Pt-Bi-Ti-Ox composite consists of 1 wt% Pt and 5 wt% Bi. The high activity of the composite is discussed on the basis of the crystalline morphology and surface composition

The catalytic activity and hydrocarbon selectivity in electrochemical carbon dioxide (CO2) reduction on cuprous oxide (Cu2O) derived copper nanoparticles is discussed. Cuprous oxide films with [100], [110] and [111] orientation and variable thickness were electrodeposited by reduction of copper(ii) lactate on commercially available copper plates. After initiation of the electrochemical CO2 reduction by these oxide structures, the selectivity of the process was found to largely depend on the parent Cu2O film thickness, rather than on the initial crystal orientation. Starting with thin Cu2O films, besides CO and hydrogen, selective formation of ethylene is observed with very high ethylene-to-methane ratios (∼8 to 12). In addition to these products, thicker Cu2O films yield a remarkably large amount of ethane. Long term Faradaic efficiency analysis of hydrocarbons shows no sign of deactivation of the electrodes after 5 hours of continuous experiment. Online mass spectroscopy studies combined with X-ray diffraction data suggest the reduction of the Cu2O films in the presence of CO2, generating a nanoparticulate Cu morphology, prior to the production of hydrogen, CO, and hydrocarbons. Optimizing coverage, number density and size of the copper nanoparticles, as well as local surface pH, may allow highly selective formation of the industrially important product ethylene.

TiO2–SiO2 mixed oxide materials were hydrothermally synthesized and the photocatalytic degradation of phenol under UV-irradiation was evaluated. We also demonstrated that varying the co-solvent, modulates the structural properties of the materials. In particular, the use of non-polar co-solvents such as toluene seemed to increase the crystallinity, surface area, and pore diameter while the crystallite size of titania seemed to change little. A comprehensive characterization using surface and bulk techniques evidenced the role of porosities, crystallinity, and Ti–O–Si linkages of the mixed oxides as significant factors that contribute to the degradation of phenol. The TiO2–SiO2 mixed oxide material prepared using only ethanol as the solvent showed 24% degradation of phenol after 120 min of irradiation whereas other mixed oxide materials degraded phenol more efficiently (57% to 100%) in the same duration of time. The higher photocatalytic activities of the mixed oxide materials prepared using non-polar solvents is attributed to a combination of factors that include higher Apparent Surface Coverages of Ti–O–Si heterolinkages, larger pore sizes, and most importantly higher crystallinities of the titania phase. Larger pore sizes enabled better transport of reactant molecules and products to and from the active sites (Ti–O–Si heterolinkages) and the higher crystallinities of the titania phase helped in minimizing the electron–hole recombination in these photocatalysts, and thus resulted in high degradation efficiencies.

Single particle analysis of individual sea spray aerosol particles shows that cations (Na(+), K(+), Mg(2+), and Ca(2+)) within individual particles undergo a spatial redistribution after heterogeneous reaction with nitric acid, along with the development of a more concentrated layer of organic matter at the surface of the particle. These data suggest that specific ion and aerosol pH effects play an important role in aerosol particle structure in ways that have not been previously recognized.

The influence of Ti–O–Si hetero-linkages in the degradation of Rhodamine B (RhB) dye over TiO2–SiO2 xerogels is exemplified by XPS analysis. We demonstrate a relationship between the percentage surface content of Ti–O–Si and the rate of photocatalytic degradation of RhB. Our detailed surface investigation revealed that the overall degradation of RhB is enhanced due to the high surface percentage content of Ti–O–Si species, high crystallinity of titania phase, and its effective dispersion on a high surface area porous silica support.

Methyl mercaptan, CH3SH, is an industrial waste as well as the reactive product of several H2 and H2S induced catalytic hydrogenation processes of COS and CS2. Its coupling into value added products is of great importance in monetizing sour natural gas. In the present work, the full theoretical cycle of catalytic CH3SH coupling to form ethene was investigated by means of density functional theory (DFT) using chabazite as a model catalyst with emphasis on the first C-C bond formation. Calculated thermodynamics were compared with those of analogous and well established CH3OH processes to identify the similarities and differences in the reactive pathways. With few exceptions, CH3SH catalytic transformations are of higher free energy when compared to those of CH3OH. The trimethylsulfonium ion, TMS, isostructural with that of the trimethyloxonium ion, TMO, is shown to be a key reactive intermediate and a thermodynamically stable species leading to ethene formation.

[Figure Presented] Chemical mechanics: Hydrogen-bonddriven self-assembly and mechanochemistry are used to facilitate supramolecular catalysis in the solid state. Mortar-andpestle grinding proves to be an efficient means to achieve co-crystal formation and turnover using a physical mixture composed of an olefin and catalytic amounts of a ditopic template (see scheme). © 2010 Wiley-VCH Verlag GmbH &. Co. KGaA.

Accurate elemental oxidation state determination for the outer surface of a complex material is of crucial importance in many science and engineering disciplines, including chemistry, fundamental and applied surface science, catalysis, semiconductors and many others. X-ray photoelectron spectroscopy (XPS) is the primary tool used for this purpose. The spectral data obtained, however, is often very complex and can be subject to incorrect interpretation. Unlike traditional XPS spectra fitting procedures using purely synthetic spectral components, here we develop and present an XPS data processing method based on vector analysis that allows creating XPS spectral components by incorporating key information, obtained experimentally. XPS spectral data, obtained from series of molybdenum oxide samples with varying oxidation states and degree of crystallinity, were processed using this method and the corresponding oxidation states present, as well as their relative distribution was elucidated. It was shown that monitoring the evolution of the chemistry and crystal structure of a molybdenum oxide sample due to an invasive X-ray probe could be used to infer solutions to complex spectral envelopes.

Ag(I) is used to form a π-stacked metal–organic solid that exhibits remarkably high electrical conductivity. The solid undergoes a single-crystal-to-single-crystal [2+2] photodimerization to generate a 1D coordination polymer with over 40% higher conductivity. The Ag(I) complex represents the first example of an increase in conductivity resulting from a [2+2] photodimerization. Density of states calculations show a higher contribution from Ag(I) ions to the valence band in the photodimerized solid, supporting the increase in conductivity.

Natural gas is envisioned as a primary source of hydrocarbons in the foreseeable future. With the abundance of shale gas, the main concerns have shifted from the limited hydrocarbon availability to the sustainable methods of CH4 conversion to fuels. This is necessitated by high costs of natural gas transportation in its native gaseous form. Conventional gas-to-liquid conversion technologies are capital and scale intensive and can hardly be envisioned in their current form to be cost efficient in the remote locations of the natural gas extraction sites. Solar energy can be utilized at the gas extraction site to perform catalytic CH4 conversion using electrons obtained via photovoltaics or directly with photons. We provide broader insight into the catalytic CH4 conversion methods that utilize renewable energy via photo(electro)catalytic processes, with particular focus on the catalytic materials used, reaction conditions and intermediates, as well as their selectivity. Based on the currently available scientific literature, we propose several hybrid catalytic CH4 conversion processes based on both conventional and renewable – photo(electro)chemical – catalysis.