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 H-2 on Cu(100) and Zn/Cu(1 00) surfaces was studied using the dipped adcluster model (DAM) combined wi th ab initio Hartree-Fock (HF) and second-order Moller-Plesset (MP2) calcul ations. On clean Cu(100) surface, our calculations show that five successiv e hydrogenations are involved in the hydrogenation of adsorbed CO2 to metha nol, and the intermediates are formate, dioxomethylene, formaldehyde, and m ethoxy. The rate-limiting step is the hydrogenation of formate to formaldeh yde, and the Cu-Cu site is responsible for the reaction on Cu(100). The rol es 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 t he dioxomethylene intermediate at the Cu-Zn site. The present comparative r esults indicate that the Cu-Zn site is the active site, which cooperates wi th the Cu-Cu site to catalyze methanol synthesis on a Cu-based catalyst. El ectron transfer from surface to adsorbates is the most important factor in affecting the reactivity of these surface catalysts. (C) 2000 John Wiley & Sons, Inc.