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Abstract: The chain growth mechanisms of Fischer–Tropsch synthesis on Fe5C2(001) were investigated at the levels of density functional theory. On the H2 and CO co-adsorbed surface, the formation of CH and CCO is the most favored initial steps. The subsequent steps of CCO coupling with C into CCCO and CCO hydrogenation into CCH2 and CHCH are competitive. Furthermore, CCH from CCH2 and CHCH dehydrogenation can couple with C to form CCCH. Since chain initiation from CO insertion obeys insertion mechanism, and chain propagation from CCH coupling obeys carbide mechanism, both mechanisms are operative and co-operative in Fischer–Tropsch synthesis. The carburized active surfaces can be regenerated and maintained by CO adsorption on the vacancy site, followed by hydrogenation into surface formyl (CHO) and successive dissociation into surface CH and O. In addition surface O can be hydrogenated into surface OH, and H2O formation from surface OH disproponation is energetically more favored than surface OH hydrogenation. [Copyright &y& Elsevier]

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 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 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]

Abstract: Spin-polarized density functional theory calculations have been performed to investigate carbon deposition and carbide formation on Fe(100) and Fe(110) at different carbon coverage. On Fe(100) with increasing carbon coverage, the most stable carbon adsorption configuration changes from surface carbon adsorption to surface carbon diffusion into subsurface, and surface carbon clustering is not favored thermodynamically. However, surface carbon clustering is more favored kinetically than carbon diffusion; and carbon diffusion into subsurface and surface carbon clustering become competitive. On Fe(110) with increasing surface carbon coverage, the most stable adsorption configuration changes from surface carbon adsorption to surface carbon diffusion into subsurface, and this process is favored both kinetically and thermodynamically, and surface carbon clustering is neither favored nor competitive. Surface carbon deposition might form on Fe(100), while carbide formation might be found on Fe(110). [Copyright &y& Elsevier]

Abstract: The reactivity of surface OH in CH4 reforming reactions was investigated by using density functional theory calculation. The key reaction pathway from CH4 into syngas by surface OH follows CH4 →CH→CHOH→CHO→CO, which is similar with the pathway induced by surface O in CO2 reforming of CH4 (CH4 →CH→CHO→CO). Surface OH decreases the possibility of CH dehydrogenation into surface carbon. Compared to surface O and OH, surface H can eliminate surface carbon deposition more efficiently. [Copyright &y& Elsevier]

Abstract: The adsorption and interaction of alkali metals (Li, Na, K, Rb and Cs) with the Fetet1-terminated Fe3O4(111) surface have been computed at the level of density functional theory. At low coverage, adsorption of alkali metals on site-1 (Oa–Oc–Od) is energetically more favorable than on site-2 (Oa–Oc–Od). Li has the strongest adsorption energy, followed by K, Rb, Cs and Na. The computed net charges show that the alkali metals can donate electrons to surface Fe and O atoms in the order of Li

Abstract: Spin-polarized density functional theory calculations were performed to investigate CO dissociation on clean and hydrogen precovered Fe(111) at 1/3 monolayer coverage. On clean Fe(111), the adsorbed CO first diffuses from the shallow-hollow site to the bridge-like site by elevating 0.20 eV in energy, and then dissociates into C and O atoms by overcoming a barrier of 1.53 eV. Interestingly, the CO dissociation process is accelerated in the presence of H2 via intermediate CHOads (COads + 2Hads → CHOads + Hads → CHads + Oads + Hads). This stepwise path is kinetically more favored with the lowest barrier of 1.17 eV. In contrast, the previously suggested paths, COads + 2Hads → Cads + Oads + 2Hads and COads + 2Hads → Cads + OHads + Hads, are not competitive due to higher barriers (1.76 and 1.79 eV, respectively). The activity of different low-index Fe surfaces toward CO is also compared. [Copyright &y& Elsevier]

Abstract: Removal of bridging sulfur from the Mo edge of a Mo20S43 cluster has been investigated at the level of density functional theory. It is found that the reductive removal of bridging sulfur is not favored energetically but becomes favorable under CO adsorption. Due to the strong adsorption, CO can help the reductive removal of surface sulfur, and in turn, the reduced Mo edge can favor and facilitate the hydrogenation process of CO. [Copyright &y& Elsevier]

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: The adsorption of isopropanol on the clean and hydrated γ-Al2O3 (100) and (110) surfaces was investigated at the level of density functional theory. It is found that isopropanol interacts with the γ-Al2O3 surface via its −OH group. The most stable adsorption site on the (100) and (110) surfaces is Al(3) and Al(4), respectively, with the −OH group of isopropanol orientated to surface oxygen atom. The computed adsorption energies correlate well with the energy level of the surface Lewis sites. On the (100) surface with OH coverage of 8.8, Al(5) is the most stable adsorption site. On the (110) surface with OH coverages of 8.9 and 11.8, Al(2) and Al(1) are the available sites for adsorption. It is to note that water has much larger adsorption energies than isopropanol on both surfaces. [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: Spin-polarized density functional theory has been used to characterize hydrogen adsorption on the Fe3C(100), Fe3C(001) and Fe3C(010) surfaces. It is found that hydrogen adsorbs dissociatively on the three surfaces. On the Fe3C(100) surface, the most stable surface species is CH at 1/3 or 2/3 monolayer, and CH4 at 1 monolayer; in contrast on the Fe3C(001) surface the most stable surface intermediates are 3-fold H at 1/3 monolayer, and CH at 2/3 monolayer, and CH4 at 1 monolayer. On the metallic Fe3C(010) surface, hydrogen adsorbs at 2-fold or 3-fold sites. The computed energetic order of hydrogen adsorption is Fe3C(100)>Fe3C(010)>Fe3C(001), and this differs from that of CO adsorption (Fe3C(010)>Fe3C(100)>Fe3C(001)). [Copyright &y& Elsevier]

Abstract: Density functional theory (DFT) calculations have been carried out on the adsorption of CO on the (100), (001) and (010) surfaces of Fe3C. Both (100) and (001) have surface iron and carbon atoms, while (010) has only surface iron atoms. At 1/5ML on (100), the most stable adsorption configuration has adsorbed CO at a three-fold site (three Fe atoms), followed by adsorbed surface ketenylidene at a four-fold site (three iron atoms and one carbon atom). At 1/6ML on (001), the most stable adsorption configuration has adsorbed CO at a four-fold site (four iron atoms). With increased coverage, adsorption at different sites becomes possible and close in energy. On the metallic (010) surface, both two-fold and three-fold adsorptions are close in energy. The electronic states of the most stable adsorption structures have been analyzed accordingly. [Copyright &y& Elsevier]

Abstract: The structures and energetics of the chemisorbed CO2, CH x species and H as well as C2H4 on the α-Mo2C(0001) surface have been computed at the GGA-RPBE level of density functional theory. It is found that CO2 adsorbs dissociately into CO and O, in agreement with the experimental finding. The adsorbed O, CH x and H species prefer the site of three surface molybdenum atoms over a second layer carbon atom (V C site). On the basis of the calculated adsorption energies of CH x and H, the sequential dehydrogenation of CH4 and the C/C coupling reaction of CH x have been discussed. [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: 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]