Theoretical Study Of The Methanol Decomposition On Cu(110) Surface With The Presence Of Water

As we all known, energy is the foundation of human existing and development. However, the excessive consumption of fossil fuels is not only lead to the energy crisis but also caused serious environmental pollution. In order to meet the world’s energy demanding and improve the adverse environmental conditions, alternative and environmentally-friendly energy resources（e.g. hydrogen energy） have received much attention. Therefore, the efficient method of hydrogen production is an important issue that we have to faced.The mechanism of methanol decomposition on Cu-based catalyst have been systematically investigated by using periodic density functional theory method with the continuum solvation slab model. Methanol decomposition mechanism on the clean Cu（110）, H₂O/Cu（110） and OH pre-adsorbed H₂O/Cu（110） surfaces are identified. Meanwhile, the influence of a secondary metal（including Pt, Pd, Ni, Mn） on Cu（110） surface with the presence of water for methanol decomposition are systematically studied and compared. Finally, we have systematically investigated the reaction of methanol decomposition on Pt doped H₂O/Cu（110） with different Pt doping ratios that in order to fully understand the influence of Pt dopant. The main conclusions obtained from our work are summarized as follows:（1） The most favorable reaction route of CH3 OH decomposition on the clean Cu（110） surface is as follows: CH3OH�'CH3O�'CH₂O�'CHO�'CO. The rate-limiting step is the formation of CH2 O from CH3 O dehydrogenation with an activation energy of 1.32 eV. For CH3 OH decomposition on the H₂O/Cu（110） surface, the main reaction route is similar to that of on the clean Cu（110） surface, the rate-limiting step is the reaction of CH3 O dehydrogenation with an activation energy of 1.17 eV. Meanwhile, two competitive pathways for the CH3 OH decomposition on the OH pre-adsorbed H₂O/Cu（110） surface are identified. One is as follows: CH3OH�'CH3O�'CH₂O�'CHO�'CO, and the other is as follows: CH3OH�'CH3O�'CH₂O�'CH₂OOH�'CH₂OO�'CHOO�' CO2. The results show that the presence of water is facilitate methanol decomposition and the pre-adsorbed OH leads to serious reaction intermediates. For OH pre-adsorbed H₂O/Cu（110） surface, the latter route is more favorable than the former from the perspective of thermodynamics and kinetics. Using the TST, the rate constants of the corresponding mainly steps of methanol decomposition under different temperature（T=473-573 K） are calculated. This further corroborates that the presence of H2 O molecules on the Cu（110） surface conducive to CH3 OH decomposition.（2） The sequential dehydrogenation of methanol（CH3OH�'CH3O�'CH₂O�'CHO�'CO） on the metal doping H₂O/Cu（110） surface are studied in the present work. Our calculation show that the metal dopants are effectively hinder the by-product of CH2 O desorption. The Pt, Pd and Ni dopants are able to promote the hydrogen formation from CH3 OH decomposition, while Mn doped is unfavorable for the reaction. The CH3 OH decomposition catalytic activity is found to decrease in the sequence: Pd-H₂O/Cu（110） > Pt-H₂O/Cu（110） > Ni-H₂O/Cu（110） > H₂O/Cu（110） > Mn-H₂O/Cu（110）. The Br?nsted- Evans-Polanyi plot for the CH3 OH dehydrogenation steps on the metal（Pt, Pd, Ni, Mn） doped and un-doped H₂O/Cu（110） surfaces are identified, and our study may be useful for design of novel Cu-based catalysis for CH3 OH decomposition.（3） The metal Pt are doping into the H₂O/Cu（110） surface with different doping ratios（9Pt、3Pt、1Pt）. when doping 1Pt, the most favorable reaction route of CH3 OH decomposition is as follows:CH3OH�'CH3O�'CH₂O�'CHO�'CO, which is similar to that of on the un-doping H₂O/Cu（110） surface. The results show that one metal Pt doping can effectively decrease the activation energy of CH3 OH decomposition. In this case, the rate-limiting step is the CH3 O dehydrogenation with an activation energy of 0.51 eV. In the case of 3Pt, the most favorable reaction route of CH3 OH decomposition is similar to that of on 1Pt-H₂O/Cu（110）. However, it is found that CH3 OH dissociate to CH3 O is the rate-limiting step with an activation energy of 0.56 eV. In the case of 9Pt doping（the first layer of the Cu（110） is entirely doped by Pt）, the most favorable reaction route is changed comparing with that of on the 1Pt and 3Pt doping H₂O/Cu（110）, which is illustrated as follows: CH3OH�'CH₂OH�'CH₂O�'CHO�'CO. The rate-limiting step is CH3 OH dehydrogenation to CH2 OH with an activation energy of 0.77 eV. Overall, the metal Pt dopant with different doping ratios on the H₂O/Cu（110） surface remarkably affect the adsorption configurations and adsorption energies of reactants and intermediates, and the most favorable reaction pathway. A small content of Pt doped into Cu（110） surface can obtain good catalytic activation considering the price of Pt. Therefore, Pt-Cu alloy catalyst can effectively lower the activation energy of CH3 OH decomposition, which might be a useful guide for rational design alloy catalysts.