Mechanism of methanol synthesis on Cu(100) and Zn/Cu(100) surfaces: Comparative dipped adcluster model study

The mechanism of methanol synthesis from CO2 and H2 on Cu(100) and Zn/Cu(100) surfaces was studied using the dipped adcluster model (DAM) combined with ab initio Hartree–Fock (HF) and second-order Møller–Plesset (MP2) calculations. On clean Cu(100) surface, our calculations show that five successive hydrogenations are involved in the hydrogenation of adsorbed CO2 to methanol, and the intermediates are formate, dioxomethylene, formaldehyde, and methoxy. The rate-limiting step is the hydrogenation of formate to formaldehyde, and the Cu–Cu site is responsible for the reaction on Cu(100). The roles of Zn on Zn/Cu(100) catalyst are to modify the rate-limiting step of the reaction: to lower the activation energies of this step and to stabilize the dioxomethylene intermediate at the Cu–Zn site. The present comparative results indicate that the Cu–Zn site is the active site, which cooperates with the Cu–Cu site to catalyze methanol synthesis on a Cu-based catalyst. Electron transfer from surface to adsorbates is the most important factor in affecting the reactivity of these surface catalysts. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 341–349, 2000