Vinyl acetate （VA） synthesis on Pd/Au（111） and Pd/Au（100） surfaces has been systematically investigated through first-principles density functional theory （DFT） calculations. The DFr results showed that for VA...Vinyl acetate （VA） synthesis on Pd/Au（111） and Pd/Au（100） surfaces has been systematically investigated through first-principles density functional theory （DFT） calculations. The DFr results showed that for VA synthesis, the ＇Samanos＇ reaction mechanism （i.e., direct coupling of coadsorbed ethylene and acetate species and subsequent/%hydride elimination to form VA） is more favorable than the ＇Moiseev＇ mechanism （i.e., ethylene first dehydrogenates to form vinyl species which then couple with the coadsorbed acetate species to form VA）. More importantly, it was found the surface coverage of acetate has a significant effect on the reactivity of VA synthesis, and the activation energy of the rate- controlling step on Pd/Au（100） surface is smaller than that on Pd/Au（111） surface （0.88 vs. 0.95 eV）, indicating the former is more active than the latter.展开更多
The adsorption properties of atomic and molecular species on Ir4/MgO and Ir4/γ-Al2O3 have been systematically studied by means of planewave density functional theory（DFT）calculations using the periodic boundary con...The adsorption properties of atomic and molecular species on Ir4/MgO and Ir4/γ-Al2O3 have been systematically studied by means of planewave density functional theory（DFT）calculations using the periodic boundary conditions.The binding energies of these species were ordered as follows：H2O〈C2H4〈H〈OH〈S〈N〈O〈C.The adsorption energies of adatoms on Ir4/MgO were larger than those on Ir4/γ-Al2O3 except hydrogen atom,but were in reverse for the molecules calculated.In addition,the difference of adsorption energies on MgO and γ-Al2O3 supports has been elucidated by analyzing the electronic properties.A detailed investigation on state density clarifies the nature of the magnitude of adsorption energy.These calculated results are consistent well with the available experimental and theoretical results.展开更多
Adsorption of cyclohexene and its dehydrogenation intermediates on the nAu/Pt（100） （n = 0, 1, 2 means clean Pt, one monolayer and two layers of Au covered Pt surfaces, respectively.） has been investigated by self-...Adsorption of cyclohexene and its dehydrogenation intermediates on the nAu/Pt（100） （n = 0, 1, 2 means clean Pt, one monolayer and two layers of Au covered Pt surfaces, respectively.） has been investigated by self-consistent （GGA-PW91） density functional theory combined with periodic slab model. It is found that on the clean platinum, there are two kinds of favorable adsorption sites, i.e., hollow sites and bridge sites, and the adsorption energy at the hollow site is larger than that at the bridge site. However, on the Au/Pt and 2Au/Pt surfaces, there are three kinds of adsorption sites, and the adsorption energies are alike at both the bridge site and the top site. The magnitude order of the adsorption energies is as follows： clean Pt Au/Pt 2Au/Pt. The configurations of cyclohexene molecule have been distorted a little during the geometry optimizations. The lengths of C–M （M = Pt or Au, on the top layer of the slab） bonds are closely related to the corresponding adsorption energies.展开更多
Ethylene epoxidation on Ag（111）, Pt（111）, Rh（111） and Mo（100） has been studied by density functional theory （DFT） calculations. The results show that the adsorption energies of possible adsorbed species invo...Ethylene epoxidation on Ag（111）, Pt（111）, Rh（111） and Mo（100） has been studied by density functional theory （DFT） calculations. The results show that the adsorption energies of possible adsorbed species involved in the ethylene epoxidation increase in the order： Ag〈Pt〈Rh〈Mo, and the activation energies of the formation of epoxide （EtO） and acetaldehyde （Ac） follow the same order. Moreover, it is found that the smallest difference in the activation energies between EtO formation and Ac formation is shown on Ag. These results indicate that the metallic Ag shows the highest between activity and selectivity for ethylene epoxidation among the studied metal surfaces. Perhaps, the stability of OMME intermediate is the crucial factor in controlling the activity and selectivity. And the stronger the binding of OMME, the lower the activity and selectivity are. In addition, the relationships between the reaction enthalpy and activation energy on these four metal surfaces are investigated, and it is found that such a correlation is only applied for OMME（a） → EtO（a） and OMME（a） → Ac（a）, while invalid for the case of C2H4（a） ＋ O（a） → OMME（a）.展开更多
The decomposition of methoxy on Cu（111）, Ag（111）, Au（111）, Ni（111）, Pt（111）, Pd（111）, and Rh（111） has been studied in detail by the density functional theory calculations. The calculated activation barri...The decomposition of methoxy on Cu（111）, Ag（111）, Au（111）, Ni（111）, Pt（111）, Pd（111）, and Rh（111） has been studied in detail by the density functional theory calculations. The calculated activation barriers were successfully correlated with the coupling matrix element V 2 ad and the d-band center （ε d ） for the group IB metals and group VIII metals, respectively. By comparison of the activation energy barriers of the methoxy decomposition on different metals, it was found that Pt is the best catalyst for methoxy decomposition. The possible reason why the metallic Pt is the best catalyst has been analyzed from both the energetic data and the electronic structure information, that is, methoxy decomposition on Pt（111） has the largest exothermic behavior due to the closest p-band center of the CH 3 O among all metals after the adsorption.展开更多
基金supported by the State Key Program of Natural Science of Tianjin (Grant No. 13JCZDJC26800)the foundation of State Key Laboratory of Coal Conversion (Grant No. J13-14-908)
文摘Vinyl acetate （VA） synthesis on Pd/Au（111） and Pd/Au（100） surfaces has been systematically investigated through first-principles density functional theory （DFT） calculations. The DFr results showed that for VA synthesis, the ＇Samanos＇ reaction mechanism （i.e., direct coupling of coadsorbed ethylene and acetate species and subsequent/%hydride elimination to form VA） is more favorable than the ＇Moiseev＇ mechanism （i.e., ethylene first dehydrogenates to form vinyl species which then couple with the coadsorbed acetate species to form VA）. More importantly, it was found the surface coverage of acetate has a significant effect on the reactivity of VA synthesis, and the activation energy of the rate- controlling step on Pd/Au（100） surface is smaller than that on Pd/Au（111） surface （0.88 vs. 0.95 eV）, indicating the former is more active than the latter.
文摘The adsorption properties of atomic and molecular species on Ir4/MgO and Ir4/γ-Al2O3 have been systematically studied by means of planewave density functional theory（DFT）calculations using the periodic boundary conditions.The binding energies of these species were ordered as follows：H2O〈C2H4〈H〈OH〈S〈N〈O〈C.The adsorption energies of adatoms on Ir4/MgO were larger than those on Ir4/γ-Al2O3 except hydrogen atom,but were in reverse for the molecules calculated.In addition,the difference of adsorption energies on MgO and γ-Al2O3 supports has been elucidated by analyzing the electronic properties.A detailed investigation on state density clarifies the nature of the magnitude of adsorption energy.These calculated results are consistent well with the available experimental and theoretical results.
基金supported by the National Natural Science Foundation of China (Grants No. 20273034, 20673063)supported by the NKStar HPC program
文摘Adsorption of cyclohexene and its dehydrogenation intermediates on the nAu/Pt（100） （n = 0, 1, 2 means clean Pt, one monolayer and two layers of Au covered Pt surfaces, respectively.） has been investigated by self-consistent （GGA-PW91） density functional theory combined with periodic slab model. It is found that on the clean platinum, there are two kinds of favorable adsorption sites, i.e., hollow sites and bridge sites, and the adsorption energy at the hollow site is larger than that at the bridge site. However, on the Au/Pt and 2Au/Pt surfaces, there are three kinds of adsorption sites, and the adsorption energies are alike at both the bridge site and the top site. The magnitude order of the adsorption energies is as follows： clean Pt Au/Pt 2Au/Pt. The configurations of cyclohexene molecule have been distorted a little during the geometry optimizations. The lengths of C–M （M = Pt or Au, on the top layer of the slab） bonds are closely related to the corresponding adsorption energies.
文摘Ethylene epoxidation on Ag（111）, Pt（111）, Rh（111） and Mo（100） has been studied by density functional theory （DFT） calculations. The results show that the adsorption energies of possible adsorbed species involved in the ethylene epoxidation increase in the order： Ag〈Pt〈Rh〈Mo, and the activation energies of the formation of epoxide （EtO） and acetaldehyde （Ac） follow the same order. Moreover, it is found that the smallest difference in the activation energies between EtO formation and Ac formation is shown on Ag. These results indicate that the metallic Ag shows the highest between activity and selectivity for ethylene epoxidation among the studied metal surfaces. Perhaps, the stability of OMME intermediate is the crucial factor in controlling the activity and selectivity. And the stronger the binding of OMME, the lower the activity and selectivity are. In addition, the relationships between the reaction enthalpy and activation energy on these four metal surfaces are investigated, and it is found that such a correlation is only applied for OMME（a） → EtO（a） and OMME（a） → Ac（a）, while invalid for the case of C2H4（a） ＋ O（a） → OMME（a）.
文摘The decomposition of methoxy on Cu（111）, Ag（111）, Au（111）, Ni（111）, Pt（111）, Pd（111）, and Rh（111） has been studied in detail by the density functional theory calculations. The calculated activation barriers were successfully correlated with the coupling matrix element V 2 ad and the d-band center （ε d ） for the group IB metals and group VIII metals, respectively. By comparison of the activation energy barriers of the methoxy decomposition on different metals, it was found that Pt is the best catalyst for methoxy decomposition. The possible reason why the metallic Pt is the best catalyst has been analyzed from both the energetic data and the electronic structure information, that is, methoxy decomposition on Pt（111） has the largest exothermic behavior due to the closest p-band center of the CH 3 O among all metals after the adsorption.
