Model Studies of Methanol Synthesis on Copper Catalysts

摘要

The synthesis of methanol by the hydrogenation of CO_2 over Zn-deposited and Zn-free copper surfaces has been studied using an XPS apparatus combined with a high-pressure flow reactor (18 atm). It was shown that the Zn deposited on Cu(111) and poly-Cu acted as a promoter for methanol synthesis, while the Zn on Cu(110) and Cu(100) had no such a promotional effect. The turnover frequency (TOF) for Zn/Cu(111) linearly increased with Zn coverage below theta_(Zn)=0.19, and then decreased above theta_(Zn)=0.20. The optimum TOF obtained at theta_(Zn)=0.19 was thirteen-fold lager than TOF for the Zn-free Cu(111) surface. On the other hand, no promotional effect of Zn was observed for the reverse water-gas shift reaction on all the surfaces. The results indicate the formation of special sites for methanol synthesis on Zn/Cu(111).