Paper HC+SS-ThA11
Methanol Partial Oxidation Catalyzed by Singly-dispersed Pd on ZnO(101¯0)

Thursday, November 10, 2016, 5:40 pm, Room 103A

Heterogeneous catalysis by singly-dispersed metal atoms on non-metallic surfaces offers great potential for maximizing the efficiency of metal atoms, and optimizing their activity and selectivity. Herein, we present results from our ab-initio density functional theory (DFT) calculations for methanol partial oxidation (MPO), an industrially important reaction for the production of H₂, on Pd₁/ZnO(101¯0). To begin with we find that the Pd atom prefers to adsorb at the oxygen vacancy site i.e. the anion vacancy is responsible for stabilizing singly-dispersed Pd atom on ZnO(101¯0). We discuss the adsorption characteristics of a set of gas molecules (CH3OH, O₂, CO, CO₂, H₂O, H₂), and the potential energy profile including activation barriers for the reaction processes associated with MPO on Pd₁/ZnO(101¯0), and compare them with those on Pd16Zn16 nanoparticle and pristine ZnO(101¯0). We find that the singly dispersed Pd sites offer a high activity towards the formation of CO₂ and H₂ over that of CO and H₂O. We trace this reactivity to the electronic structure of the single Pd site as modified by its local environment which in turn facilitates a strong binding of CO to the Pd site, thereby increasing the CO desorption barrier and stabilizing O₂ on ZnO(101¯0), which is essential for further oxidation steps. With activation energy barriers and pre-exponential factors calculated from DFT, for a large set of reaction intermediates, we perform kinetic Monte Carlo simulations to determine the turn over frequencies and rate limiting steps in the formation of CO₂ and H₂ on Pd1/ZnO(101¯0), under ambient conditions.

Work supported in part by DOE grant DE-FG02-07ER15842.