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Based on the density functional theory together with a periodic model, the adsorption and successive dissociation of water on clean and X (X = C, N and O)-covered Cu(111) surfaces have been investigated systematically. Our results indicate that the doping of carbon, nitrogen and oxygen atoms on the clean Cu(111) surface strengthens the interaction of H 2 O-surface and weakens the interaction of OH-surface. The corresponding adsorption configurations of adsorbates are slightly changed. Compared to that on clean Cu(111) surface, it is revealed that the doped C, N and O atoms can promote the catalytic activity of H 2 O dissociation and that the adsorbed C and N atoms are beneficial for the dissociation of OH, namely, the joining of C and N atoms on Cu(111) surfaces improve the catalytic activity and selectivity for H 2 O complete dissociation. Among four types Cu(111) surfaces, C-covered Cu(111) is the most favorable surface both kinetically and thermodynamically. [ABSTRACT FROM AUTHOR]

The study of formic acid decomposition on transition metal surfaces is important to obtain useful information for vapor phase catalysis involving HCOOH and for the development of direct formic acid fuel cells. In this study, periodic density functional theory calculations have been employed to investigate the dissociation pathways of HCOOH on Cu (111) surface. About adsorption, it is found that the adsorption of HCOO, COOH, HCO, CO, OH and H on Cu (111) are considered chemisorption, whereas HCOOH, CO 2 , H 2 O and H 2 have the weak interaction with Cu (111) surface. Furthermore, the minimum energy pathways are analyzed for the decomposition of HCOOH to CO 2 and CO through the scission of H O, C H and C O bonds. It is found that HCOOH, HCOO and COOH prefer to dissociate in the related reactions rather than desorb. For the decomposition, it is indicated that HCO and COOH are the main dissociated intermediates of trans -HCOOH, CO 2 is the main dissociated intermediates of bidentate-HCOO, and CO is the main dissociated product of cis -COOH. The co-adsorbed H atom is beneficial for the formation of CO 2 from cis -COOH. Besides, it is found that the most favorable path for HCOOH decomposition on Cu (111) surface is HCOOH-HCO-CO (Path 5), where the step of CO formation from HCO dehydrogenation is considered to be the rate-determining step. The results also show that CO is preferentially formed as the dominant product of HCOOH on Cu (111) surface. [ABSTRACT FROM AUTHOR]

The adsorption and successive dehydrogenation mechanisms of NH 3 on Pd-Cu (1 1 1) and Cu-Pd (1 1 1) surfaces (the Pd atoms substitution of the first and second layers of Cu (1 1 1) surfaces) have been systematically investigated by density functional theory (DFT) method with a periodic slab model. All possible adsorption configurations of relevant intermediates on Pd-Cu (1 1 1) and Cu-Pd (1 1 1) surfaces are identified. It is revealed that the adsorption configurations and corresponding adsorption energies of adsorbates are slightly changed on Pd-Cu (1 1 1) and Cu-Pd (1 1 1) surfaces. The adsorption energies of NH x (x = 0–3) species exhibit the following trend: NH 3 < NH 2 < NH < N. Then, the minimum energy path for the complete dehydrogenation of NH 3 into adsorbed N and H is identified to explore the dehydrogenation mechanisms on different surfaces. The highest energy barrier and reaction energy on Pd-Cu (1 1 1) surface are greatly reduced to 1.56 and 0.99 eV, implying that the complete dehydrogenation of NH 3 on Pd-Cu (1 1 1) surface is favorable both kinetically and thermodynamically, namely, the doped-Pd atoms in the first layer are the reaction active center. Compared to that on clean Pd (1 1 1) and Cu (1 1 1) surfaces, it is found that the synergistic effect exits in different layers of catalyst surfaces. The calculated results show that the layer-substituted Pd atoms on the surface of Cu catalysts exhibit a better catalytic activity for NH 3 dehydrogenation compared to the clean Cu (1 1 1) surface. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) method was employed to investigate the adsorption and decomposition mechanisms of CH 3 OH on Pd (100) surface. Different kinds of possible adsorption modes of relevant intermediates on the surface were identified. It was found that CH 3 OH and CH 2 OH prefers to adsorb on the top site, CH 3 O, CHOH and CO occupy preferentially on the bridge site, while CH 2 O, CHO, COH and H species adsorb on the hollow site. The adsorption energies of all species exhibit the following trend: CH 3 OH < CH 2 O < CH 3 O < CO < CH 2 OH < H < CHO < CHOH < COH. Subsequently, four possible dissociation pathways of CH 3 OH via initial O H and C H bond scissions were proposed and studied systematically. The transition states, energy barriers and reaction energies were calculated to explore the dehydrogenation mechanisms of CH 3 OH on Pd (100) surface. It was indicated that the scission of C H bond is more favorable for CH 3 OH and CH 2 OH and the H O bond cleavage is easier for CHOH. The path 2 (CH 3 OH CH 2 OH CHOH CHO CO) is the most possible dehydrogenation pathway, where the highest energy barrier of CH 3 OH dissociation makes it to be the rate-determining step of the whole dehydrogenation reaction. [ABSTRACT FROM AUTHOR]

Using density functional theory (DFT) together with periodic slab models, the adsorption and dehydrogenation mechanisms of methane on clean and oxygen-covered Pd (1 0 0) surfaces have been studied systematically. Different adsorption geometries were investigated for CH 4 and related intermediates (CH 3 , CH 2 , CH, C, H, O and OH). It was found that CH 4 and CH 3 prefer to adsorb on the top site, CH 2 and OH are favorable on the bridge site, while CH, C, O and H species adsorb preferentially on the hollow site. In addition, this work identified the stable co-adsorption configurations for the relevant co-adsorption groups. It was concluded that the effect of co-adsorbed oxygen atom tends to weaken the adsorbate–substrate interaction on the Pd (1 0 0) surface. Finally, transition states, energy barriers and reaction energies were determined to confirm the mechanism of dehydrogenation of CH 4 on clean and oxygen-covered Pd (1 0 0) surfaces. The existence of oxygen atom increases the energy barriers obviously and inhibits the dissociation of CH x ( x = 1, 2 and 4) except for CH 3 group. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO 2 ) hydrogenation to methanol is a promising method for the activation and conversion of CO 2 . Density functional theory (DFT) calculations were carried out to explore the reaction mechanisms on PdCu 3 (111) surface. The stable adsorption structures of all possible intermediates were evaluated, showing that the interaction between saturated species and PdCu 3 (111) surface are much weaker than that of unsaturated species. Three possible pathways of forming formate (HCOO) and hydrocarboxy (COOH) and reverse water gas shift (RWGS) followed by CO hydrogenation have been considered. The H 2 COO formation is kinetically and energetically prohibited with the highest activation barrier and reaction energy of 1.84 and 1.26 eV, indicating HCOO pathway is highly unlikely to occur. In addition, the byproducts of HCOOH and HCHO can be formed in this route. The rate-limiting steps of HCOH ∗ hydrogenation in COOH route and cis -COOH ∗ dissociation in RWGS + CO-Hydro route need to overcome almost the same barriers of ∼1.40 eV. However, the byproduct of HCOOH ∗ exists in the latter route. Furthermore, the effect of H 2 O which is a reaction product of methanol synthesis has been also discussed. It is shown that H 2 O not only enhances the adsorption of intermediates involved in rate-limiting steps but also reduces the kinetics of rate-limiting steps, especially in COOH pathway. The COOH pathway of CO 2  →  trans -COOH →  t,t -COHOH →  t,c -COHOH →  c,c -COHOH → COH → HCOH → H 2 COH → CH 3 OH is found to be the most favorable. The calculated results provide a potential candidate for methanol synthesis and the present insights are helpful for CO 2 conversion and utilization with Pd-Cu bimetallic catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Isomerization pathway of N -ethylcarbazole hydrogenation products was explained for the first time. • Synergy of SMSI and MSAI for the loading of Ru was preliminarily discussed. • Ru on Zr-based support exhibited remarkable catalytic hydrogenation activity. N -ethylcarbazole (NEC) is a widely studied liquid organic hydrogen carrier, and a large number of catalysts with excellent reactivity has been designed and developed thus far. However, the phenomenon of isomeric transformation of 12H-NEC products during the reaction was not explained. Here, we studied the process based on three different Ru catalysts supported on zirconium-based supports, and based on the experimental results, we identified that supported metal-support strong interaction (SMSI), metal-support anion interaction (MSAI) and hydrogen spillover will have coupling effect on the hydrogenation reaction path and the occurrence of isomerization in 12H-NEC product. Higher 12 [H] B content in 12H-NEC under Ru/ZrN catalyst was caused by the large number of secondary active centers on the surface of the support reacting in the hydrogenation reaction. The active site for the isomerization of 12 [H] B to 12 [H] A may be the electronegativity interface formed by Ru and the support, while the electroneutral or electropositive interface rich in hydrogen is not conducive to the catalytic conversion. To sum up, an image model for the isomeric transformation of 12H-NEC products was proposed. [ABSTRACT FROM AUTHOR]

Employing density functional theory (DFT) together with periodic slab models, the adsorption and dehydrogenation of H 2 O on clean and oxygen-covered Au (1 0 0) have been investigated systematically. On the basis of the theoretical analysis, the favorable adsorption sites and stable configurations of all species were clarified. H 2 O was predicted to adsorb weakly on the top, bridge, hollow sites, with the top site preferred. Whereas OH and atomic O prefer to adsorb on the hollow site and H occupies the bridge site. What's more, this work displayed the optimum configurations for the relevant co-adsorption groups. The results elucidated that co-adsorption is apt to impair the interaction of adsorbate-substrate due to the joining of oxygen atom except for H 2 O molecule. Eventually, the interrelated transition states and activation energies were calculated to explore the dehydrogenation mechanism of H 2 O. A feasible mechanism on oxygen pre-covered surfaces for complete dehydrogenation of H 2 O was also presented. It was illuminated that atomic oxygen could diminish the barrier energy substantially of the first dissociation step and play a pivotal role in the decomposition of H 2 O molecule. [ABSTRACT FROM AUTHOR]

Highlights: [•] Dehydrogenation mechanism of H2S on clean and S-covered Au (100) was firstly studied using periodic DFT calculations. [•] The optimized structures and adsorption energies were obtained. [•] The results give the performance of using atomic sulfur to modified Au (100) surface. [•] The energy barriers and reaction energies were calculated. [ABSTRACT FROM AUTHOR]

Highlights: [•] Dehydrogenation mechanism of H2O on Pd (100) was studied using periodic DFT calculations. [•] The optimized structures and adsorption energies were obtained. The results offered an explanation to use oxygen to modify Pd (100) surface. The energy barriers and reaction energies were calculated. [ABSTRACT FROM AUTHOR]

Highlights: [•] Dehydrogenation mechanism of NH3 on Pd (111) was studied using periodic DFT calculations. [•] The optimized structures and adsorption energies of NH x were obtained. [•] The results offered an explanation to use Pd as dehydrogenation catalysts. [•] We calculated the energy barriers and reaction energies by periodic calculations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Dehydrogenation mechanism of CH4 on Pd (111) was studied using periodic DFT calculations. [•] The optimized structures and adsorption energies of CH x were obtained. [•] The results offered an explanation to use Pd as dehydrogenation catalysts. [•] We firstly calculated the energy barriers and reaction energies by periodic calculations. [Copyright &y& Elsevier]

• Reaction mechanisms for CO 2 hydrogenation to methanol on (ZrO 2) 3 /Cu(1 1 0) interface were studied by DFT. • The adsorption energies of unsaturated species are increased on (ZrO 2) 3 /Cu(1 1 0) interface. • The (ZrO 2) 3 /Cu(1 1 0) interface greatly increases the selectivity toward CH 3 OH. • CH 3 OH is mainly produced via HCOOH channel in the reaction scheme on ZrO 2 /Cu(1 1 0) interface without byproducts. The hydrogenation of carbon dioxide (CO 2) to methanol on (ZrO 2) 3 /Cu(1 1 0) interface has been investigated by periodic density functional theory (DFT) calculations. With regard to the adsorption of all the species involved in methanol synthesis, the species prefer to adsorb on the interface between Cu(1 1 0) surface and (ZrO 2) 3 cluster and through C-Cu and O-Zr bonds. The adsorption energies of unsaturated species are increased on (ZrO 2) 3 /Cu(1 1 0) interface compared to that on Cu(1 1 0) surface. Formate (HCOO), hydrocarboxy (COOH) and reverse water gas shift (RWGS) pathways in the reaction network of C O 2 + 3 H 2 → C H 3 OH + H 2 O were considered. In HCOO pathway, the binding CO 2 * primarily hydrogenates to bi -HCOO*, which hydrogenates subsequently to HCOOH*, H 2 COOH*, H 2 CO*, H 3 CO* and CH 3 OH*. The formation of H 2 CO* and OH* through H 2 COOH* decomposition has the highest reaction barrier of 1.39 eV, which is lower than the rate-limiting step of cis -COOH* dissociation with an activation barrier of 1.46 eV in RWGS pathway. COOH* is facile to go through HCOOH* intermediate comparing with the formation of t,t -COHOH* in COOH pathway, indicating that CH 3 OH is mainly produced via HCOOH channel in the reaction scheme on ZrO 2 /Cu(1 1 0) interface. The formation of byproducts such as HCOOH, H 2 CO and CO is significantly inhibited over (ZrO 2) 3 /Cu(1 1 0) interface, showing a high selectivity for producing CH 3 OH. These results demonstrated that (ZrO 2) 3 /Cu(1 1 0) is a potential candidate catalyst for methanol production via CO 2 hydrogenation. [ABSTRACT FROM AUTHOR]