Methanol synthesis by hydrogenation of CO2 over a Zn-deposited Cu(111): formate intermediate

The role of Zn in the promotion of methanol synthesis over Cu surfaces was studied by elucidating effects of Zn on both synthesis and decomposition of formate species using XPS. The initial formation rate of formate over Zn-free Cu(111) was measured to be 7.6 x 10(-4) molecules site(-1) s(-1) at P-H2 = P-CO2 = 380 Torr and 353 K. The rate of formate synthesis over Zn-deposited Cu(111) was the same as that on Zn-free Cu(111), indicating that formate species were synthesized on copper surfaces and Zn had no promotional effect on the formate synthesis. On the other hand, the surface formate species on Zn-deposited Cu(111) decomposed at a temperature higher than that on Zn-free Cu(111) by similar to 50 K, suggesting that Zn deposited on Cu(111) created special sites stabilizing formate species. These results suggested that the role of Zn on methanol synthesis by the hydrogenation of CO2 is to stabilize the formate intermediate, and to promote a hydrogenation process of formate species. (C) 1997 Elsevier Science B.V.