First-Principles Study on the Origin of the Different Selectivities for Methanol Steam Reforming on Cu(111) and Pd(111)

Methanol steam reforming (MSR) is an important industrial process for hydrogen production, and fundamental understanding of the reaction mechanism is crucial to improve the catalytic activity and selectivity. In the present work, we present a comparative mechanistic study of the MSR reaction on two key model systems, Cu(111) and Pd(111), with distinct selectivity using density functional theory calculations. We find that, on Cu(111), methanol dehydrogenation to formaldehyde is favorable first through the O-H bond scission, and the final products are dominated by carbon dioxide and hydrogen. On Pd(111), formaldehyde is also found to be an important intermediate; however, it comes through the C-H bond breaking first, and the final products are mainly CO and hydrogen. We find that the distinct selectivity on the Cu( Ill) and Pd(Ill) surfaces originates from the different reactivities of HCHO on the two surfaces. On Cu(111), HCHO tends to react with the hydroxyl to form hydroxymethoxy followed by its decomposition to CO2. In contrast, direct dehydrogenation of HCHO to CO is favorable on Pd(111). Finally, we find that there is a good linear correlation between the transition-state energies and the final-state energies for the elementary reactions involved in the MSR reaction, which may be useful for computational design and optimization of the catalysts.