A model catalyst for methanol synthesis: Zn‐deposited and Zn‐free Cu surfaces

The synthesis of methanol by the hydrogenation of CO2 over Zn‐deposited and Zn‐free single‐crystal copper surfaces has been studied using an x‐ray photoelectron spectroscopy apparatus combined with a high‐pressure flow reactor (18 atm). The order of plane for the catalytic activity was (110)≳(311)≳(100)≳(111) for Zn‐free copper surfaces. The Zn‐deposited Cu(111) (ΘZn=0.19) was 13 fold more active than the Zn‐free Cu(111). The activation energy for the methanol synthesis (73–84 kJ/mol) was close to each other regardless of the surface structure or the presence of Zn. It was shown that the Zn deposited on Cu(111) acted as a promoter for the methanol synthesis, while the Zn on Cu(110) and Cu(100) had no such a promotional effect. On the postreaction surfaces of Zn‐deposited and Zn‐free copper samples, a small amount of formate species was always detected which was more stable than that on clean Cu surfaces. This formate species’s coverage was proportional to the activity for methanol formation. © 1996 American Vacuum Society