Reaction mechanisms of methanol synthesis from CO/CO2 hydrogenation on Cu2O(111): Comparison with Cu(111)

A systematic theoretical study was performed to investigate methanol synthesis from CO/CO2 hydrogenation and the water-gas-shift (WGS) reaction on Cu(111) and Cu2O(111) surfaces using density functional theory (DFT) and kinetic Monte Carlo (KMC) simulations. Specifically, DFT was used to investigate methanol synthesis from CO/CO2 hydrogenation on these surfaces at P = 80 atm, T= 553 K and (CO+ CO2)/H-2 = 20/80. The results show that methanol can be synthesized from CO or CO2 hydrogenation and is dependent on the catalyst's preparation as well as the active site type. Further, CO is the main carbon source when the surface is predominantly covered by Cu+ species. However, CO2 is the primary carbon source when metallic Cu covers the surface. Under the reaction conditions investigated, H-2 and CO easily reduce Cu2O to metallic Cu, and the Cu+ species are stabilized by the presence of H2O, CO2, carrier (such as MgO) or alkali metals. For this reason, the scale of methanol produced from CO or CO2 hydrogenation depends on the ratio of Cu+/Cu-0.