Mechanism of methanol decomposition on the Pd/WC(0001) surface unveiled by first-principles calculations

Abstract

In this study, the decomposition of methanol into the CO and H species on the Pd/tungsten carbide (WC)(0001) surface is systematically investigated using periodic density functional theory (DFT) calculations. The possible reaction pathways and intermediates are determined. The results reveal that saturated molecules, i.e., methanol and formaldehyde, adsorb weakly on the Pd/WC(0001) surface. Both CO and H prefer three-fold sites, with adsorption energies of – 1.51 and – 2.67 eV, respectively. On the other hand, CH3O stably binds at three-fold and bridge sites, with an adsorption energy of – 2.58 eV. However, most of the other intermediates tend to adsorb to the surface with the carbon and oxygen atoms in their sp3 and hydroxyl-like configurations, respectively. Hence, the C atom of CH2OH preferentially attaches to the top sites, CHOH and CH2O adsorb at the bridge sites, while COH and CHO occupy the three-fold sites. The DFT calculations indicate that the rupture of the initial C-H bond promotes the decomposition of CH3OH and CH2OH, whereas in the case of CHOH, O-H bond scission is favored over the C-H bond rupture. Thus, the most probable methanol decomposition pathway on the Pd/WC (0001) surface is CH3OH → CH2OH → trans-CHOH → CHO → CO. The present study demonstrates that the synergistic effect of WC (as carrier) and Pd (as catalyst) alters the CH3OH decomposition pathway and reduces the noble metal utilization.