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Abstract: The direct and H-mediated dissociation of CO2 on Ni(211) were investigated at the level of density functional theory. Although formate (HCOO) formation via CO2 hydrogenation was widely reported for CO2 adsorption on metal surfaces, it is found that on Ni(211) HCOO dissociation into CHO and O is much difficult, while direct dissociation of adsorbed CO2 into CO and O is more favorable. It is also found that the degree of electron transfer from surface to adsorbed CO2 correlates with the elongation of C–O bond lengths and the reduction of the CO2 dissociation barrier. [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]

On the basis of spin-polarized periodic density functional theory including the latest dispersion correction (PBE-D3), the mechanisms of H 2 , O 2 , H 2 O, CO 2 , CO, CH 4 and C 2 H x dissociative adsorption on the hexagonal Mo 2 C surface have been computed. In our study we used the metallic Mo 2 C(001) surface as well as the Mo 2 C(101) surface with Mo/C = 1/1 ratio. It is found that the dissociative adsorptions of these small molecules are exothermic and have low barriers; and the Mo 2 C(001) surface has much stronger dissociative adsorption than the Mo 2 C(101) surface. In contrast to the Mo 2 C(001) surface, OH + H and O + 2H can form equilibrium on Mo 2 C(101) surface. For C 2 H x dissociative adsorption on the Mo 2 C(001) surface, C H bond dissociation is kinetically much more favorable than the C C bond dissociation, and the optimum C 2 H 6 dissociation route follows the order of C 2 H 6 → CH 3 CH 2 + H → C 2 H 4 + 2H → CH 2 CH + 3H → C 2 H 2 + 4H → C 2 H + 5H→ C 2 + 6H. Due to the very strong dissociative adsorption energies, both surfaces can be oxidized easily by using H 2 O; and high oxygen coverage can be expected. The Mo 2 C(001) surface can uptake more surface O atoms than the Mo 2 C(101) surface. These surfaces can also be carburized by using CH 4 , albeit in less extent. On the surface with co-adsorbed CO 2 + 4H; CO 2 dissociation (CO 2 → CO + O → C + 2O) is more favorable than the hydrogenation of CO 2 (CO 2 + H → HCOO or COOH) and CO (CO + H → HCO or COH). It is noted that CO 2 hydrogenation towards CH 4 formation is unlikely on the Mo 2 C(001) surface, while the effective barrier of surface C hydrogenation on the Mo 2 C(101) surface can be reduced by 2O and 2OH pre-covered surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Density functional theory calculations have been carried out on the reaction of ketene hydrogenation on Fe5C2(001) for the understanding of the Fischer–Tropsch synthesis mechanism. The main reaction pathway of ethene formation is CsH2CO→CCsH2 →CHCsH2 →CH2CsH2, and ethane formation follows CsH2CO→CCsH2 →CCsH3 →CCsH3 →CHCsH3 →CH2CsH3 →CH3CsH3, while that of ethanol is CsH2CO→[CsH3CO and/or CsH2CHO]→CsH3CHO→CsH3CH2O→CsH3CH2OH. Detailed comparison shows clearly that ketene dissociation with the formation of hydrocarbons is more favorable than the stepwise hydrogenation with the formation of ethanol. The expected product should be hydrocarbons rather than ethanol, in agreement with the experimental observation. [Copyright &y& Elsevier]

[Display omitted] • CO 2 hydrogenation over inverse supported Zr 9 O 18 /Ni(1 1 1) nanocatalyst was computed. • Charge transfer from Ni(1 1 1) to supported Zr 9 O 18 nanoparticle has been found. • Supported Zr 9 O 18 nanoparticle has coordinatively unsaturated Zr sites at interface. • H 2 prefers dissociative adsorption on Ni(1 1 1) and CO 2 activation prefers interface Zr sites. • Surface HCOO is the most important intermediate and methanol is the selective product. To tune the activity and selectivity of CO 2 hydrogenation, inverse supported Zr 9 O 18 /Ni(1 1 1) catalysts are designed based on ab initio molecular dynamics simulation and density functional theory calculation under the consideration of the number of interfacial O and Zr atoms as well as the interaction between O and Zr atoms. For the most stable catalyst with coordinatively unsaturated interface Zr sites, charge transfer from surface to oxide has been found. The Ni(1 1 1) surface is pre-covered by H atoms and the interface Zr sites can activate CO 2 to a large extent, and their interaction results in the spontaneous formation of surface formate. Further hydrogenation of surface formate leads to the selective formation of methanol with an apparent Gibbs free energy barrier of 0.62 eV, lower than that of methane formation (1.09 eV). On the contrary to metallic nickel and supported nickel catalysts, the most favoured methanol formation route [HCOO → CHO → CH 2 O → CH 3 O → CH 3 OH] does not involve CO as intermediate, revealing the mediated interface effect. [ABSTRACT FROM AUTHOR]

• Coverage-dependent CO hydrogenation was computed and compared. • At 0.25 reasonable coverage CO dissociation prefers H-assisted path leading to CH formation. • Apparent barrier of methanation is in close agreement with experimental value. • Ketene is the intermediate from CH 2 and CO coupling for the first C-C bond formation. • CH 3 C is the homologue of CH and starts the cycle for chain propagation. For the first time the full catalytic cycle of CO activation, methanation and first C-C bond formation on Fe(110) at high coverage [0.25 ML, p (2 × 2)] have been computed by density functional theory. Under thermodynamic equilibrium, H-assisted CHO formation and CHO dissociation into CH+O are preferred thermodynamically and kinetically. Then CH can be transformed into methane via successive hydrogenation; and the first C-C bond can be formed by CH 2 and CO coupling resulting in ketene (CH 2 CO), which can be hydrogenated to acetyl (CH 3 CO). The next C-O dissociation of CH 3 CO results in CH 3 C (higher homologue CH), and this starts C-C chain growth and catalytic cycle. Both methanation and chain growth have the same rate-determining step as CHO dissociation. The computed apparent barrier of methanation is much close to experimental value. These high coverage results clearly explain the experimentally observed formation of methane as well as high hydrocarbons of synthesis gas conversion on metallic Fe surface. The computed vibrational frequencies of the proposed surface intermediates agree with the experimental data. This high coverage strategy should be applicable to other heterogeneous catalytic reactions having coverage preferences. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Novel Cu/ZnO-Al 2 O 3 composites had been constructed and applied in furfural hydrogenation to produce furfuryl alcohol in a fixed-bed reactor. As the result, conversion of FFA over Cu/ZnO catalyst (within 16–24 h TOS) could be improved from 84.9% to 98.0% at 120 °C and 51.4% to 72.1% at 100 °C with a high selectivity of FOL (≈98%) over the novelly constructed Cu/ZnO-Al 2 O 3 catalyst. The role of Al components derived from different precursors like Al(NO 3 ) 3 , as-prepared Al(OH) 3 and pseudo-boehmite had been systemically investigated by various techniques such as XRD, Raman spectroscopy, H 2 -TPR, N 2 O titration, XPS, AES experiments and confirmed to be both improving dispersion of copper/zinc species and hindering Cu-ZnO interaction of the aurichalcite derived catalysts. Preparation of the industrial Cu/ZnO-Al 2 O 3 catalysts had been revealed and explained more clearly. [ABSTRACT FROM AUTHOR]

The mechanisms of CO hydrogenation with the formation of C 1 surface species on the clean and K 2 O-doped χ-Fe 5 C 2 (111) surfaces with carbon vacancies have been comparatively elucidated. On both surfaces, CO direct dissociation (CO → C + O) is not favored. On the clean surface, the preferred H-assisted pathway is CO → HCO → CH 2 O → CH 3 O → CH 3 OH. On the K 2 O-doped surface, the preferred paths are HCO → CHOH → CH + OH and HCO → CH 2 O → CH 2 OH → CH 2 + OH due to the barrier decrease of the C O bond cleavage of COH, CHOH and CH 2 OH by K 2 O promotion. These results might explain the K 2 O promoted carburization process and the formation of long-chain hydrocarbons. [ABSTRACT FROM AUTHOR]

The effect of Cu promoter on CH 4 formation from CO hydrogenation on Fe(100) has been investigated using spin-polarized density functional theory computations on periodic slab models. Two pathways of CH 4 formation are considered: (a) direct dissociation of CO followed by successive C hydrogenation and (b) successive hydrogenation of CO followed by deoxygenation of CH x O (x = 1–3). On the clean and Cu doped surfaces, direct dissociation of CO followed by successive C hydrogenation is more favorable kinetically and the overall CH 4 formation is endothermic. Compared with the clean surface, the Cu doped surface can suppress CH 4 formation by raising the barrier from the co-adsorbed CO + 4H. Methanol formation is unfavorable on both surfaces kinetically and thermodynamically. Reversely, methanol decomposition is favorable. It is also noted that Cu doping lowers the adsorption ability of the Fe(100) surface and therefore the adsorption energies of all species on the potential energy surfaces. [ABSTRACT FROM AUTHOR]

The hydrogenation of dimethyl oxalate (DMO) to ethanol involves the stepwise hydrogenation of C O bonds and hydrogenolysis of C O bonds. In the present work, the assembly of ternary active sites (Cu, ZrO 2 , Al 2 O 3 sites) for this reaction was investigated. The calcination temperature was demonstrated to have profound influences on the catalytic performance, evolutions of texture and structure properties and functionality of active phases of the ternary catalysts with similar compositions. The Cu/ZrO 2 /Al 2 O 3 catalyst calcined at a high temperature of 750 °C exhibited an ethanol yield up to 97.4% and stable performance (>200 h). Key to success is the concurrence of the stable metallic Cu sites with more proportions of Cu + sites, active crystalline ZrO 2 phases and sufficient acid sites which were generated upon high temperature calcination. The high-temperature calcination annealed Cu particles into large ones, facilitating the high stability. Another factor for the good stability is the formation of CuAl 2 O 4 spinel and the resulted strong interactions between Cu and Al 2 O 3 after reduction. Overall, the design of efficient multifunctional catalysts for hydrogenation/hydrogenolysis of C O/C O bonds lies in the adequate assembly and modulation of textural, structural and surface properties of catalysts. The structure-performance relationships were well elucidated by the analysis of structural and surface properties of active phases and catalytic performance, which provide more rational choices for making high-performance catalysts for C O hydrogenation and C O hydrogenolysis reactions. [ABSTRACT FROM AUTHOR]

Abstract: The reactivity of furfural and its reaction intermediates is separately investigated in a fixed-bed reactor over a commercial catalyst (C1: Cu/Zn/Al/Ca/Na=59:33:6:1:1, atomic ratio) and a self-made multicomponent one (C2: Cu/Cr/Ni/Zn/Fe=43:45:8:3:1, atomic ratio). Some interesting results are obtained in this work. Firstly, both furfural and furfuryl alcohol can eliminate carbon monoxide to produce furan. Secondly, tetrahydrofuran and 2-methyltetrahydrofuran are all very stable, and n-butanol mainly derives from furan rather than tetrahydrofuran. Thirdly, 2-pentanone, 2-methyltetrahydrofuran, 1-pentanol and 2-pentanol are all the hydrogenation products of 2-methylfuran. Finally, with C2 catalyst containing the Ni element, the main reaction product of tetrahydrofurfuryl alcohol is tetrahydofuran, while δ-valerolactone is the main product with C1 one. This work has unified some conflicting mechanisms and discussed the origin of some interesting products, which is important to understand the mechanism and reaction pathway of furfural hydrogenation, and to provide an instruction for the design of new catalytic formulations. [Copyright &y& Elsevier]

Abstract: The kinetics models of oxygenate formation in Fischer–Tropsch synthesis (FTS) over an industrial Fe–Mn catalyst are studied in a continuous spinning basket reactor. Detailed kinetics models on the basis of possible oxygenate formation mechanisms, namely adsorbed CO or CH2 insertion mechanisms, are derived. The calculated alcohol and acid distributions in FTS reaction fit the experimental data well with considering the esterification reactions between alcohols and acids. The alcohol formation via successive hydrogenation of intermediate [RCO-s] is more energetically favorable than the acid formation via the reaction between the [RCO-s] and [OH-s]. The alcohol formation is not via the successive hydrogenation of acid intermediates over the Fe–Mn catalyst under FTS reaction conditions. [Copyright &y& Elsevier]