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Although the effect of CeO2 morphology on catalytic properties has been studied, research interests mainly focus on the oxidation reactions while the effect of CeO2 morphology on other reactions, such as dehydrogenation reaction, has rarely been reported. In this study, the dehydrogenation of ammonia borane (AB) was chosen as a model reaction to study the effect of CeO2 morphology (“c”, “r” and “o” denote cube, rod, and octahedron, respectively) on the catalytic properties of Ru/CeO2. Our study shows that the activity follows the order of Ru/c-CeO2 > Ru/r-CeO2 > Ru/o-CeO2, which is different from the order observed in other catalytic oxidation reactions. X-ray photoelectron spectroscopy (XPS), Raman and H2-Temperature program reduction (H2-TPR) measurements reveal that there is a weak interaction between Ru and c-CeO2, and metallic Ru is the dominant species in Ru/c-CeO2, which are possibly responsible for the highest catalytic activities among three Ru/CeO2 catalysts. [ABSTRACT FROM AUTHOR]

Abstract: The reaction mechanism of thiophene hydrodesulfurization (HDS) on a Mo3S9 model catalyst has been investigated at the GGA level of density functional theory. On the basis of the computed energetic data, 2,5-dihydrothiophene has been identified as the most important intermediate of HDS processes, and it is responsible for the direct formation of butadiene as the principal product. Neither the stepwise formation of cis-2-butene nor that of butane is competitive. However, butene (or butane) can be obtained from the hydrogenation of the formed butadiene. [Copyright &y& Elsevier]

Abstract: The entire catalytic hydrodesulfurization (HDS) cycle of benzothiophene over Mo3S9 cluster has been investigated at the level of density functional theory. It is found that the hydrogenation and hydrogenolysis route with dihydrobenzothiophene (DHBT) as intermediate is more favored than the hydrogenolysis and hydrogenation route with styrene as intermediate. The stepwise hydrogenolysis of SB–C9 (C(aryl)–S) bond in DHBT leading to the formation of 2-phenylethanethiol is more favored than that of SB–C2 (C(alkyl)–S) bond with 2-ethylthiophenol as intermediate. The computed activation free energy and rate constant of benzothiophene hydrogenation to DHBT agree well with the available experimental data. The difference in HDS reactivity between benzothiophene and thiophene has been discussed. [Copyright &y& Elsevier]

The catalytic performance of Cu/ZrO2 calcined at different temperatures was investigated with XRD and XPS. It was found that the activity of Cu/ZrO2 depends on the interaction between copper and zirconia, rather than on their crystal sizes. The XRD and XPS results illustrated that the reinforced interaction between copper and zirconia can hinder the increase of the copper crystal size in the reaction process. In addition, B3LYP/LACVP density functional calculation revealed electron transfer from copper to zirconia and weakening effect of surface hydroxyl on zirconia near copper center. [Copyright &y& Elsevier]

• The mechanism for eliminating adsorbed oxygen by the reduction with H and CO on χ-Fe 5 C 2 surfaces was investigated. • The removal mechanism shows diversity over different facets. • Carbon-rich surface exhibits higher barriers to direct CO 2 formation, like (110) and (111). The removal of surface oxygen adsorbed on iron carbides is essential to protect the nanoparticle from oxidation in heterogeneous catalysis. Herein, we explored the removal of pre-adsorbed oxygen on seven facets of χ-Fe 5 C 2, and four pathways including both direct and indirect routes for generating H 2 O and CO 2 were investigated. The removal mechanism shows diversity over different facets. On (010), the formation of CO 2 through the reaction between surface oxygen and adsorbed CO is more favorable. While on (510), (001), (110), (11-1) and (-411), the elimination in the form of H 2 O through OH disproportionation dominates. In particular, surface oxygen can be removed facilely either in H 2 O or CO 2 on (111) surface. What's more, surface with more carbons exhibits higher barriers to direct CO 2 formation, like (110) and (111). Our work provides knowledge about mechanism of O removal and CO 2 formation, which may be helpful in protecting the nanoparticle from further oxidation. Graphical Abstract [Display omitted]. [ABSTRACT FROM AUTHOR]

Abstract: The detailed transformation mechanism of methacrolein with methanol to methyl methacrylate over Pd was investigated by density functional theory (DFT) calculation as an attempt to gain more insight into the oxidative esterification reaction. The entire catalytic cycle and reaction energies are computed for various possible paths over Pd20 cluster. It is found that the hydrogen elimination of MAL following acyl group reaction with methoxyl appears to be an energetically favorable pathway in catalyst cycle. The formation of unsaturated alcohol by H addition, and that of saturated aldehyde through the Cn by methoxyl and H are also competitive. The formation of hemiacetal intermediate is not necessary for the production of MMA. [Copyright &y& Elsevier]

Abstract: Hydrogen adsorption on the Fetet1- and Feoct2-terminated Fe3O4(111) surfaces has been computed at the level of density functional theory. At 2/5 monolayer (ML), the most favored hydrogen adsorption on the Fetet1-terminated surface is homolytic and dissociative on surface O atoms, while other adsorption modes become possible at higher coverages. On the Feoct2-terminated surface at 1/3 ML, hydrogen prefers to adsorb heterolytically and dissociatively on surface Fe and O atoms, while other adsorption modes become in close energy at 2/3 and 1 ML. The Fetet1-terminated surface is more favored than the Feoct2-terminated surface for hydrogen adsorption. The adsorption mechanism has been analyzed on the basis of the calculated local density of state. [Copyright &y& Elsevier]

Abstract: A series of Cu–Mn–Si catalysts for synthesis of cyclohexanone (CHN) and 2-methylfuran (2-MF) through the coupling of cyclohexanol (CHL) dehydrogenation and furfural (FFA) hydrogenation were prepared by co-precipitation method. The catalysts were characterized by using N2 physisorption, X-ray diffraction (XRD), H2 temperature programmed reduction (H2-TPR), N2O-chemisorption and ammonia temperature-programmed desorption (NH3-TPD) methods. The results show that metal–silica/or metal–metal interactions are presented in the catalysts, and the contents of copper, manganese and silicon affect the BET surface area, acidity and copper dispersion. The results of the catalytic tests indicate that manganese increases the activity of CHL dehydrogenation and FFA hydrogenation as well as the selectivity of 2-MF. A Cu–Mn–Si catalyst including appropriate copper, manganese and silicon is found to be most active, selective and stable under reaction conditions. [Copyright &y& Elsevier]

Abstract: FeCu/SiO2 catalysts, in which K or Na promoter is incorporated respectively, are prepared by a combination method of continuous co-precipitation and spray drying technology. The catalysts were characterized by temperature-programmed desorption and Mössbauer spectroscopy. The Fischer–Tropsch synthesis (FTS) performance of the catalysts was studied in a continuously stirred tank slurry reactor. The basicity of the K-promoted catalyst is enhanced, as demonstrated by CO2-TPD results. MES results show that sodium can weaken the dispersion of α-Fe2O3 phase; either potassium or sodium can promote carburization of the catalyst, while the effect of sodium is weaker. FTS results indicate that the addition of K or Na can improve the catalyst activity, and shift the product distribution to heavy hydrocarbons to the different extent. [Copyright &y& Elsevier]

Abstract: A 24T model containing a complete two-layered 12-membered ring connected by an 8-membered side pocket was used to represent the channel of the MOR framework. On the basis of this model, the structures of the acid sites in the main channels of Li- and Na-MOR as well as their interaction with pyridine probe molecule were investigated using the ONIOM2 (QM/QM; B3LYP/6-31G(d,p):HF/3-21G) and ONIOM2 (QM/MM; B3LYP/6-31G(d,p):UFF) methods. There are two stable structures for the Li-MOR cluster; one has Li+ interacting with two oxygen atoms around Al, and the other has Li+ interacting with four oxygen atoms belonging to a five-membered ring. This four-fold Li+ coordination is consistent with Na+ in Na-MOR, and is the same as the Na+ coordination in the intersection model of Na-ZSM-5. The ONIOM2 (QM/MM) method overestimates the adsorption energies of pyridine (195.0/192.8 and 170.6kJ/mol for Li-MOR and Na-MOR, respectively), while the ONIOM2 (QM/QM) method gives reasonable results (171.6/154.7 and 131.3kJ/mol, respectively) compared to the available experimental values (153–195 and 120kJ/mol, respectively). The structural parameters of the adsorption complexes showed that coordination of the alkali ion to the nitrogen atom of pyridine dominates the overall interaction between the zeolite and pyridine, and the adsorption complexes were further stabilized by hydrogen bonding between the hydrogen atoms of pyridine and the lattice oxygen atoms of the zeolite framework. [Copyright &y& Elsevier]

Abstract: Density functional theory computations have been carried on the hydrogen adsorption mechanism on a Mo27S54 single layer cluster, which has a size (15–20Å) close to that of real catalysts. For one molecule of H2 adsorption, the most stable adsorption form (E ads =−27.2kcal/mol) is the homolytic dissociation on the S edge with the hydrogen atoms keeping away from the plane consisting of all Mo atoms, followed by the heterolytic dissociation (E ads =−26.1kcal/mol) on the intersection of S and Mo edges with the formation of Moc–H and Sc–H bonds. At high coverage with two and three H2, however, dissociated hydrogen adsorption on the Mo sites are much more favored thermodynamically than on the S sites. Moreover, the corner sites are more favored thermodynamically for hydrogen adsorption and formation of coordinatively unsaturated sites than the edge sites. In addition, the activation energy of H2 dissociation and hydrogen transfer processes have been computed to be 2.7–19.2kcal/mol, and these rather low barriers indicate the enhanced mobility of the adsorbed hydrogen on the surface. [Copyright &y& Elsevier]

Abstract: A comprehensive Fischer–Tropsch synthesis (FTS) kinetics model including the hydrocarbon and oxygenate formation reactions as well as water gas shift (WGS) reaction over an Fe–Mn catalyst is developed in a continuous spinning basket reactor. On the basis of CH2 insertion alkyl mechanism, the kinetics expressions for paraffins, olefins, alcohols and acids are derived. Kinetics calculation results indicate that the formation of paraffins, olefins, alcohols and acids over the Fe–Mn catalyst are parallel competitive reactions. Reasonable and strict analysis in mathematics is given to interpret the results which the comprehensive kinetics model cannot predict the olefin/hydrocarbon ratio well though the olefin readsorption and secondary reactions are involved in the kinetics model. Oxygenates might readsorb over the catalyst surface and take part into the corresponding secondary reactions (chain growth and hydrogenation to the corresponding hydrocarbons), which leads to the exponentially decrease of the experimental alcohol/hydrocarbon and acid/hydrocarbon ratios with the increase of carbon number. [Copyright &y& Elsevier]