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Abstract: The interaction of Cu n (n =1–4) cluster with the dehydrated γ-Al2O3(110), hydrated γ-Al2O3(110) and dehydrated γ-Al2O3(100) surfaces has been systematically investigated to illustrate the influence of the hydroxylation of γ-Al2O3 surfaces on the stability and growth of Cu for Cu/γ-Al2O3 catalyst. Here, we present the main results obtained by the density functional theory together with slab model calculations. Our results show that the adsorption of Cu n (n =2–4) cluster on the γ-Al2O3(110) surface is more stable than that on the γ-Al2O3(100) surface, for the single Cu atom, the reverse becomes true. For the γ-Al2O3(110) surface, the adsorption of Cu n (n =2–4) cluster on the dehydrated surface is more stable than that on the hydrated surface due to the presence of the surface hydroxyls, however, the adsorption of the single Cu atom on the hydrated surface is more stable than that on the dehydrated surface due to the larger Cu–support interaction energy. On the other hand, compared to the γ-Al2O3(100) surface, the γ-Al2O3(110) surface is more favorable for the growth of Cu n clusters, in which the presence of surface hydroxyls reduces the growth ability of Cu n clusters. [Copyright &y& Elsevier]

Abstract: The sulfurization mechanism of H2S on the ZnO(100) surface during the desulfurization of coal gas was investigated by using periodic density functional theory (DFT) calculations. The adsorption of H2S, SH, atomic S, and atomic H, as well as the coadsorption of SH and an H atom, and the coadsorption of S and two H atoms, were initially examined to identify energetically favorable intermediates. Potential energy profiles for three paths of H2S−ZnO(100) interactions producing H2 and H2O were obtained, respectively. Our results show that H2S is preferred to dissociatively adsorb on the ZnO(100) surface, followed by dehydrogenation process to form sulfur species. Molecular-level calculations demonstrate that H2O formation via the H2S−ZnO interaction is the most probable reaction pathway both kinetically and thermodynamically. ZnO has double functions during the desulfurization of H2S. One is as a catalyst to accelerate the dissociation of H2S, while the other is as the reactant participating in the reaction of H2S with ZnO to form H2O. [Copyright &y& Elsevier]

Abstract: The mechanisms of CH x (x =1-3) formation from CO hydrogenation on Cu(111) surface have been systematically investigated using periodic density functional calculations. The activation barriers and reaction energies for all the elementary steps involved in CH x (x =1-3) formation is presented here. CO hydrogenation and its dissociation have been discussed. Our results show that the CO dissociation route is less energetically favored on Cu(111) surface than CO hydrogenation to form CHO and COH, in which CO mainly goes through hydrogenation to form CHO, meanwhile, the formation of CHO is more favorable both kinetically and thermodynamically than that of COH. Starting from CHO, we further investigate the formation of CH x (x =1-3), two conditions, without H-assisted and with H-assisted, are considered. As a result, we seek out the optimal paths of CH x (x =1-3) formation and the corresponding activation barrier of rate-controlled step on Cu(111) surface, moreover, among all CH x (x =1-3) species, CH2 and CH3 are the most favored monomer for CO hydrogenation on Cu(111). In addition, our results show that CH3OH is also easily formed by CO hydrogenation, and the formations of CH2, CH3 and CH3OH by CO hydrogenation compete with each other on Cu(111) surface. [Copyright &y& Elsevier]

Abstract: The interaction mechanism of H2S with different Cu2O(111) surfaces, including perfect, oxygen-vacancy and sulfur-containing surfaces, have been systematically studied using periodic density functional calculations. Different kinds of possible modes of H2S, as well as the resultant SH and S species adsorbed on these surfaces are identified. Two types of pathways via molecular and dissociative adsorption processes are mapped out. Our results show that sulfur species (H2S, SH and S) interact with surface Cu centers; H2S exists in the form of molecular adsorption on perfect and sulfur-containing surfaces; the dissociative adsorption of H2S occurs predominantly on oxygen-vacancy surface, suggesting that oxygen-vacancy exhibits a strong catalytic activity toward the dissociation of H2S. On the other hand, the dissociation processes of the molecular and dissociative adsorption H2S, leading to final product S species on these Cu2O(111) surfaces, show that the overall dissociation process is exothermic. Meanwhile, with respect to molecular adsorption H2S, the activation barrier and reaction energy of the overall dissociation process on perfect and oxygen-vacancy surfaces indicate that H2S can easily dissociate into S species. Importantly, in the case of dissociative adsorption of H2S, the dissociation of H2S into S species is a spontaneous process with respect to molecular adsorption H2S. However, on sulfur-containing surface, the presence of surface S atom goes against the Heaking process both thermodynamically and kinetically. Finally, the vibrational frequencies for the adsorbed H2S, SH and S species on these surfaces have been obtained, which can be applied to guide surface vibrational spectroscopy in experiment. [Copyright &y& Elsevier]

Abstract: A density-functional theory method has been conducted to investigate the dissociation of CH4 on NiCu (111) surface. Two models: uniform surface slab model (Model A) and Cu-rich surface slab model (Model B) have been constructed to represent the NiCu (111) surface, in which the ratio of Ni/Cu is unit. The obtained results on the two models have been compared with those obtained on pure Ni (111) and Cu (111). It is found that the adsorption of CH x (x =1–3) on Model B are weaker than on Model A. The rate-determining steps of CH4 dissociation on Model A and B both are the dissociation of CH, and the corresponding activation barriers are 1.37 and 1.63eV, respectively. Obviously, it is approximately equal on Model A to that on pure Ni (111) [H. Liu, R. Zhang, R. Yan, B. Wang, K. Xie, Applied Surface Science 257 (2011) 8955], while it is lower by 0.58eV on Model B compared to that on pure Cu (111). Therefore, the Cu-rich surface has better carbon-resistance ability than the uniform one. Those results well explain the experimental facts that NiCu/SiO2 has excellent catalytic performance and long-term stability [H.-W. Chen, C.-Y. Wang, C.-H. Yu, L.-T. Tseng, P.-H. Liao, Catalysis Today 97 (2004) 173], however, there is serious carbon deposition on NiCu/MgO–Al2O3 in CO2 reforming of methane [J. Zhang, H. Wang, A. K. Dalai, Journal of Catalysis 249 (2007) 300]. [Copyright &y& Elsevier]

Abstract: A density functional theory slab calculations of CH4 dissociation on Pt(h k l) surfaces have been systematically presented. On the basis of the energetic analysis, the favorable adsorption sites and stable configurations of CH x (x =0–4) and H species on Pt(111), Pt(110) and Pt(100) surfaces are first obtained, respectively. Afterwards, the most stable configurations of coadsorbed CH x /H(x =0–3) are located. Further, the kinetic and thermodynamical results of CH4 dissociation on Pt(h k l) surface suggest that CH is the most abundant CH x species. Our results mean that Pt catalyst can resist the carbon deposition in the CH4 dissociation, which can give a microscopic reason that why Pt catalyst can lead to lower carbon deposition and show a high activity in the reaction related to CH4. [Copyright &y& Elsevier]

A theoretical analysis about the mechanism and kinetics of dimethyl carbonate (DMC) formation via oxidative carbonylation of methanol on Cu2O catalyst is explored using periodic density functional calculations, both in gas phase and in solvent. The effect of solvent is taken into account using the conductor-like screening model. The calculated results show that CO insertion to methoxide species to produce monomethyl carbonate species is the rate-determining step, the corresponding activation barrier is 161.9 kJ mol−1. Then, monomethyl carbonate species reacts with additional methoxide to form DMC with an activation barrier of 98.8 kJ mol−1, above reaction pathway mainly contributes to the formation of DMC. CO insertion to dimethoxide species to form DMC is also considered and analyzed, the corresponding activation barrier is 308.5 kJ mol−1, suggesting that CO insertion to dimethoxide species is not competitive in dynamics in comparison with CO insertion to methoxide species. The solvent effects on CO insertion to methoxide species involving the activation barriers suggest that the rate-determining step can be significantly affected by the solvent, 70.2 kJ mol−1 in methanol and 63.9 kJ mol−1 in water, which means that solvent effect can reduce the activation barrier of CO insertion to methoxide species and make the reaction of CO insertion to methoxide in solvents much easier than that in gas phase. Above calculated results can provide good theoretical guidance for the mechanism and kinetics of DMC formation and suggest that solvent effect can well improve the performance of DMC formation on Cu2O catalyst in a liquid-phase slurry. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The hydrolysis mechanism of CS was studied using density functional theory. By analyzing the structures of the reactant, transition states, intermediates, and products, it can be concluded that the hydrolysis of CS occurs via two mechanisms, one of which is a two-step mechanism (CS first reacts with an HO, leading to the formation of the intermediate COS, then COS reacts with another HO, resulting in the formation of HS and CO). The other is a one-step mechanism, where CS reacts with two HO molecules continuously, leading to the formation of HS and CO. By analyzing the thermodynamics and the change in the kinetic function, it can be concluded that the rate-determining step involves H and OH in HO attacking S and C in CS, respectively, causing the C=S double bond to change into a single bond. The two mechanisms are competitive. When performing the hydrolysis of CS with a catalyst, the optimal temperature is below 252°C. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The interaction processes of trace amounts of N-methyl-2-pyrrolidinone (NMP), CS/NMP (1:1 by volume) and pure NMP solvent with the hydrogen bond of OH⋯N in coal were constructed and simulated by density functional theory methods. The distances and bond orders between the main related atoms, and the hydrogen bond energy of OH⋯N were calculated. The calculated results show that pure NMP solvent does not weaken the hydrogen bond of OH⋯N in coal. However, trace amounts of NMP and CS/NMP (1:1 by volume) have a strong capacity to weaken the hydrogen bond of OH⋯N in coal. The H2-N3 distances are elongated from 1.87 Å to 3.80 Å and 3.44 Å, the bond orders of H2-N3 all disappear, and the corresponding hydrogen bond energies of OH⋯N in coal decrease from 45.72 kJ mol to 7.06 and 11.24 kJ mol, respectively. These results show that CS added to pure NMP solvent plays an important role in releasing the original capacity of NMP to weaken the hydrogen bond of OH⋯N in coal, in agreement with experimental observations. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption and dissociation of O2 on CuCl(111) surface have been systematically studied by the density functional theory (DFT) slab calculations. Different kinds of possible modes of atomic O and molecular O2 adsorbed on CuCl(111) surface and possible dissociation pathways are identified, and the optimized geometry, adsorption energy, vibrational frequency and Mulliken charge are obtained. The calculated results show that the favorable adsorption occurs at hollow site for O atom, and molecular O2 lying flatly on the surface with one O atom binding with top Cu atom is the most stable adsorption configuration. The O–O stretching vibrational frequencies are significantly red-shifted, and the charges transferred from CuCl to oxygen. Upon O2 adsorption, the oxygen species adsorbed on CuCl(111) surface mainly shows the characteristic of the superoxo (O2 −), which primarily contributes to improving the catalytic activity of CuCl, meanwhile, a small quantity of O2 dissociation into atomic O also occur, which need to overcome very large activation barrier. Our results can provide some microscopic information for the catalytic mechanism of DMC synthesis over CuCl catalyst from oxidative carbonylation of methanol. [Copyright &y& Elsevier]

Abstract: A density-functional theory method has been conducted to investigate the association of C+O on (111) facets of ordered NiCo alloy and the results have been compared with those obtained on pure Ni(111) surface. In reaction of C+O, the favorable reaction path is that C adsorbed on HCP-1 site moves to the nearest Ni–Co bridge site, and associates with O migrating from FCC-1 site to result in CO adsorbed on the bridge site of Ni–Co. However, the reaction barrier is higher by 0.35eV than that on pure Ni(111), which indicates that the incorporation of Co into the Ni crystal is not in favor of the reaction of carbon delimination. [Copyright &y& Elsevier]

Abstract: A density-functional theory method has been conducted to investigate the adsorption of CH x (x =0–4) as well as the dissociation of CH x (x =1–4) on (111) facets of ordered NiCo alloy. The results have been compared with those obtained on pure Ni (111) surface. It shows that the adsorption energies of C and CH are decreased while it is increased for CH3 on NiCo (111) compared to those on pure Ni (111). Furthermore, on NiCo (111), dissociation of CH x prefers not to the top of Ni, but to the top of Co. The rate-determining step for CH4 dissociation is considered as the first step of dehydrogenation on NiCo (111), while it is the fourth step of dehydrogenation on Ni (111). Furthermore, the activation barrier in rate-determining step is slightly higher by 0.07eV on Ni (111) than that on NiCo (111). From above results, it is important to point out that carbon is easy to form on NiCo (111) although the adsorption energy of C atom is slightly decreased compared to that on Ni (111). [Copyright &y& Elsevier]

Abstract: Based on density functional theory, together with COSMO (conductor-like solvent model) in Dmol3, the solvent effects on both the Cu2O(111) surface properties and the adsorption of CO on Cu2O(111) surface have been systematically investigated. Different dielectric constants, including vacuum, liquid paraffin, methylene chloride, methanol and water, are considered. The solvent effect on Cu2O(111) surface properties shows that the solvent favors Cu2O(111) surface area growth. The adsorption of CO on Cu2O(111) surface indicates that the structural parameters and adsorption energies of CO are very sensitive to the COSMO solvent model. Solvent effects can effectively improve the stability of CO adsorption on Cu2O(111) surface and the case of C–O bond activation. The interaction of solvent molecules with Cu2O(111) surface is compared with that of CO with Cu2O(111). Results suggest that the solvent effect is the dominating cause for the interaction of CO with Cu2O(111) surface in solvent, in which Cu2O(111) shows higher catalytic activity for CO activation. But the solvent may be not the only reason promoting CO activation. These analyses give us some new insights into the understanding of solvent effects. [Copyright &y& Elsevier]

Abstract: The adsorption and dissociation of O2 on the perfect and oxygen-deficient Cu2O(111) surface have been systematically studied using periodic density functional calculations. Different kinds of possible modes of atomic O and molecular O2 adsorbed on the Cu2O(111) surface are identified: atomic O is found to prefer threefold 3Cu site on the perfect surface and Ovacancy site on the deficient surface, respectively. CuCUS is the most advantageous site with molecularly adsorbed O2 lying flatly over singly coordinate CuCUS–CuCSA bridge on the perfect surface. O2 adsorbed dissociatively on the deficient surface, which is the main dissociation pathway of O2, and a small quantity of molecularly adsorbed O2 has been obtained. Further, possible dissociation pathways of molecularly adsorbed O2 on the Cu2O(111) surface are explored, the reaction energies and relevant barriers show that a small quantity of molecularly adsorbed O2 dissociation into two O atoms on the deficient surface is favorable both thermodynamically and kinetically in comparison with the dissociation of O2 on the perfect surface. The calculated results suggest that the presence of oxygen vacancy exhibits a strong chemical reactivity towards the dissociation of O2 and can obviously improve the catalytic activity of Cu2O, which is in agreement with the experimental observation. [Copyright &y& Elsevier]

Abstract: Interactions of atomic and molecular hydrogen with perfect and deficient Cu2O(111) surfaces have been investigated by density functional theory. Different kinds of possible modes of H and H2 adsorbed on the Cu2O(111) surface and possible dissociation pathways were examined. The calculated results indicate that OSUF, CuCUS and Ovacancy sites are the adsorption active centers for H adsorbed on the Cu2O(111) surface, and for H2 adsorption over perfect surface, CuCUS site is the most advantageous position with the side-on type of H2. For H2 adsorption over deficient surface, two adsorption models of H2, H2 adsorbing perpendicularly over Ovacancy site and H2 lying flatly over singly-coordinate Cu–Cu short bridge, are typical of non-energy-barrier dissociative adsorption leading to one atomic H completely inserted into the crystal lattice and the other bounded to CuCUS atom, suggesting that the dissociative adsorption of H2 is the main dissociation pathway of H2 on the Cu2O(111) surface. Our calculation result is consistent with that of the experimental observation. Therefore, Cu2O(111) surface with oxygen vacancy exhibits a strong chemical reactivity towards the dissociation of H2. [ABSTRACT FROM AUTHOR]

The reaction mechanisms of H with OCS have been investigated theoretically by using density function theory method. Three possible pathways leading to major products CO and HS, as well as two possible pathways leading to by-product CH have been proposed and discussed. For these reaction pathways, the structure parameters, vibrational frequencies and energies for each stationary point have been calculated, and the corresponding reaction mechanism has been given by the potential energy surface, which is drawn according to the relative energies. The calculated results show that the corresponding major products CO and HS as well as by-product CH are in agreement with experimental findings, which provided a new illustration and guidance for the reaction of H with OCS. [ABSTRACT FROM AUTHOR]

Abstract: DFT calculations have been performed to investigate the effect of dielectric responses of the solvent environment on the CO adsorption over CuCl(111) surface by using COSMO (conductor-like solvent model) model in Dmol3. Different dielectric constants, including vacuum, liquid paraffin, methylene chloride, methanol and water solution, are considered. The effects of solvent model on the structural parameters, adsorption energies and vibrational frequency of CO adsorption over CuCl(111) surface have been investigated. The calculation results suggest that solvent effects can improve the stability of CO adsorption and reduce the intensity of C–O bond, which might mean that solvent is in favor of C–O bond activation and improve the reaction activity of oxidative carbonylation in a slurry reactor. [Copyright &y& Elsevier]

Abstract: CH4 dehydrogenation on Rh(111), Rh(110) and Rh(100) surfaces has been investigated by using density functional theory (DFT) slab calculations. On the basis of energy analysis, the preferred adsorption sites of CH x (x =0–4) and H species on Rh(111), Rh(110) and Rh(100) surfaces are located, respectively. Then, the stable co-adsorption configurations of CH x (x =0–3) and H are obtained. Further, the kinetic results of CH4 dehydrogenation show that on Rh(111) and Rh(100) surfaces, CH is the most abundant species for CH4 dissociation; on Rh(110) surface, CH2 is the most abundant species, our results suggest that Rh catalyst can resist the carbon deposition in the CH4 dehydrogenation. Finally, results of thermodynamic and kinetic show that CH4 dehydrogenation on Rh(100) surface is the most preferable reaction pathway in comparison with that on Rh(111) and Rh(110) surfaces. [Copyright &y& Elsevier]

The hydrogen transfer reaction is one of the main source of byproducts alkanes from methanol to aromatics resulting in reducing the aromatics selectivity. The hydrogen transfer reactions between two linear alkenes were systematically investigated utilizing the density functional theoretical method on clean H-ZSM-5 and [GaH]2+ from Ga modified ZSM-5. The results show that the [GaH]2+ species on Ga-ZSM-5 is favorable for the hydrogen transfer reaction in MTA. In addition, TOF of hydrogen transfer decreases with the increase of temperature on [GaH]2+ from Ga-ZSM-5. The insights in this work will be of great significance to understand the hydrogen transfer mechanism catalyzed by metal modified zeolite. [Display omitted] • [GaH]2+ is favorable for hydrogen transfer reaction. • The mechanisms of hydrogen transfer reactions on clean and Ga modified ZSM-5 are elucidated. • TOF of hydrogen transfer decreases with the increase of temperature on [GaH]2+ from Ga-ZSM-5. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • CO oxidative coupling on Pd 4 /TiO 2 and Pd 4 /TiO 2 -O v were studied by DFT method. • The stronger interaction between Pd 4 and TiO 2 -O v than Pd 4 and TiO 2. • Pd 4 /TiO 2 -O v exhibits a high activity for CO oxidative coupling to DMO. Abstract The reaction mechanisms for CO oxidative coupling to DMO on Pd 4 supported on TiO 2 (0 0 1) catalysts were studied by using the density functional theory calculations with a Hubbard U correction (DFT + U). Two different supports including perfect TiO 2 (0 0 1) and oxygen vacancy TiO 2 (0 0 1) were investigated. The interaction between Pd 4 and supports showed that the binding energy of Pd 4 cluster with oxygen vacancy TiO 2 (0 0 1) was stronger than that with the perfect TiO 2 (0 0 1), and the relatively weak adsorption energy of CO was obtained on Pd 4 /TiO 2 -O v , implied that it was easier for CO removing and reacting. In addition, reaction mechanisms of CO oxidative coupling to DMO on Pd 4 /TiO 2 and Pd 4 /TiO 2 -O v were studied, and the Pd 4 /TiO 2 -O v catalyst showed higher activity than Pd 4 -TiO 2. Moreover, compared with Pd(1 1 1), Pd 4 /TiO 2 -O v not only reduced the amount of Pd, but also improved the activity of CO oxidative coupling to DMO. However, DMO and DMC were competitive products on Pd 4 /TiO 2 and Pd 4 /TiO 2 -O v , showed that they were with poor selectivity to DMO. [ABSTRACT FROM AUTHOR]

Abstract: The regeneration mechanisms of the sulfurized and oxygen-deficient ZnO(100) surfaces in an oxygen atmosphere have been systematically studied by using the density functional theory (DFT) method. An activation energy of 36.79kJ·mol−1 is needed for the regeneration of the sulfurized ZnO(100) surface at the GGA–PW91 functional level. The formed SO2 lies on the ZnO(100) surface horizontally, S in SO2 bonds to a surface oxygen atom to form an analogical SO3 structure. Two regeneration mechanisms are studied for the oxygen-deficient ZnO(100) surface. One is that O2 dissociatively adsorbs on the oxygen-deficient ZnO(100) surface leading to the regeneration of the surface. The other is that O2 molecularly adsorbs on the oxygen-deficient ZnO(100) surface, then a little activation energy of 29.43kJ·mol−1 is needed to make the surface regenerate. It can be concluded that the sulfurized and oxygen-deficient ZnO(100) surfaces are easy to be regenerated in an atmosphere containing O2. [Copyright &y& Elsevier]