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Abstract: The catalytic hydrodesulfurization (HDS) reactions of COS and CS2 with Mo3S9 cluster have been systematically investigated as a part of HDS of industrial feedstocks by DFT-based method. A detailed description of mechanisms is given, and different pathways are discussed and compared. It is found that the S in COS and CS2 will be hydrogenated, and the reactions will lead to formations of H2S, CO and CS. Comparing with COS, CS2 reacts with lower activation free energy and shows more reaction activity. [Copyright &y& Elsevier]

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 mechanism of thermal CO2 reforming of CH4 was investigated using the B3LYP density functional method and the CCSD(T) ab initio approach. It is found that the C–H bond dissociation of CH4 initiates the thermal chain reactions at 1200 K. CO2 does not dissociate at 1200 K, but reacts with CH3 to produce the most likely CH3O intermediate. Further degradation of the CH3O intermediate leads to the principal products of reforming, H2 and CO. The CHxO reaction path is more favored than the CHx alternatives. [Copyright &y& Elsevier]

The structure and bonding of copper carbonyl complexes, [Cu(CO)n]0/+/−, have been investigated at density functional levels of theory. It was found that the bond parameters and CO bond dissociation energy are very sensitive to the size of the employed basis set. The best agreement between theory and the available experimental data has been achieved at the B3LYP level with the cc-pVTZ/TZV2P basis set. [Copyright &y& Elsevier]

The potential energy surface of the C2HF2O and C2F3O radicals were computed at the B3LYP density functional and the CCSD(T) ab initio levels of theory. For C2HF2O radical, the resonance dominating methyl radical (HFC⋅–CF&z.dbnd6;O) is found to the most stable isomer, followed by the difluoro acetyl ([F2HCC&z.dbnd6;O]⋅) isomer by 9.9 kcal/mol. However, the most stable C2F3O radical isomer is trifluoro acetyl radical ([F3CC&z.dbnd6;O]⋅), followed by the methyl isomer (F2C⋅–CF&z.dbnd6;O) by 1.8 kcal/mol. Both acetyl radicals are relatively stable towards dissociation of being endothermic with low barriers, while other transformations (cyclization, hydrogen, and fluorine arrangements) are endothermic and have very high barriers. [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]

Abstract: In Fischer–Tropsch synthesis (FTS), the prepared catalyst hematite (α-Fe2O3) originates from goethite (α-FeOOH) dehydration in calcinations process. The structure of α-FeOOH and its topotactic transformation into α-Fe2O3 under 300–900K have been modeled within the framework of density functional theory. Molecular dynamics simulations show that the transformation begins preferentially on the surface and the dehydration is associated with the formation of voids. The loss of H2O in α-FeOOH does not modify the morphology extremely with respect to that of the original α-FeOOH. The transformation process involves hydrogen migration with the formation of adsorbed water, followed by desorption of the water molecule. The calculated barriers for hydrogen migration (118kJ/mol) and water desorption (82kJ/mol) suggest a direct reaction path without the formation of intermediates. [Copyright &y& Elsevier]

Abstract: Kinetic Monte Carlo simulations were carried out for Fischer–Tropsch synthesis in a wide range of industrially relevant reaction conditions. The macroscopic performance of different reaction conditions obtained from simulations quite agrees with experimental trends. In all examined conditions, H and CO are dominant species on catalyst surface. The rest intermediates only exist in small amount, and are controlled by H and CO coverages. Activity and selectivity for Fischer–Tropsch synthesis and water gas shift reaction are determined by surface H/CO ratio. Reaction conditions can directly change surface coverage of H, CO, and vacant sites, and consequently exert an influence on macroscopic performance of iron catalyst. [Copyright &y& Elsevier]

Abstract: The structure and stability of the neutral cages (M12O36 and M18O54, M=Mo and W) of the Keggin and Wells-Dawson anions have been investigated at the level of density functional theory. These neutral cages can be viewed topologically as polyhedra containing triangles (f 3) and squares (f 4). The relative stability of these polyhedra is determined by the location and separation of the f 3, and the α-Keggin cage without fused triangles (N33=0) is, therefore, more stable than the β isomer with N33=3. This rule is also applicable to the Wells-Dawson cages. The structures and stabilities of these neutral cages mimic those of fullerenes within the framework of isolated pentagon rule. [Copyright &y& Elsevier]

Abstract: The structure and stability of the α/β-[AlW12O40]5− anions have been investigated with seven density functional based methods. It has been found that the relative stability of these anions are sensitive to the density functionals, and the α isomer is more stable than the β one in both gas phase and simulated aqueous medium. This conclusion has also been supported by further calculations on the relative stability of the highly charged α/β-[XW12O40] y− (X=Fe(III), Co(III), Zn(II)) anions. The BP86 incorrect assignment of the α/β-[XW12O40]5− (X=Al, Ga) stability in gas phase can be attributed to the insufficient functional. [Copyright &y& Elsevier]