CO hydrogenation on stepped Cu and CuZn alloy surfaces:Competition between methanol synthesis and methanation pathways

Comprehensive fundamental understanding of CO hydrogenation reactions over Cu and ZnCu alloy surfaces is of great importance.Herein,we report a comparative DFT calculation study of elementary surface reaction network of CO hydrogenation reactions on stepped Cu(211),Cu(611),ZnCu(211) and ZnCu(611)surfaces.On Zn Cu(211) and Zn Cu(611) surfaces,the energetic favorable reaction path of CO hydrogenation reaction follows CO^(*)→HCO^(*)→H_(2)CO^(*)→H_(3)CO^(*)→CH_(3)OH^(*)→CH_(3)OH with H_(3)CO^(*)hydrogenation as the rate-limiting step and proceeds more facilely on ZnCu(611) surface than on ZnCu(211) surface.On Cu(211) and Cu(611) surfaces,the energetic favorable reaction path of CO hydrogenation reaction follows CO^(*)→HCO^(*)→HCOH^(*)→H_(2)COH^(*)→H_(3)COH^(*)→CH_(3)^(*)→CH_(4)^(*)→CH_(4) with H_(2)COH^(*) hydrogenation as the rate-limiting step and proceeds more facilely on Cu(611) than on Cu(211).The key difference of CO hydrogenation reaction on Zn Cu alloy surface and Cu is that the resulting CH_(3)OH^(*) species desorbs to produce CH_(3)OH on ZnCu alloy but undergoes H^(*)-assisted decomposition to CH_(3)^(*) and eventually to CH_(4) on Cu surface.These results successfully unveil elementary surface reaction networks and structure sensitivity of Cu and Zn Cu alloy-catalyzed CO hydrogenation reactions.