Mechanistic insight into surface oxygen species of the polyoxometalate-supported Pd single-atom catalysts for highly efficient CO oxidation

Abstract

Carbon monoxide (CO) oxidation is an important model reaction frequently studied in catalysis and environmental decontamination. Although temperature-dependent CO oxidation has been confirmed experimentally, the computational studies on the activity impact of temperature on this process have rarely been investigated. The chemically nonequivalent surface oxygen atoms (Ob and Oc) of phosphotungstic acid (PTA) will be activated by introducing metal atoms, which could achieve catalytic CO oxidation via the Mars-van Krevelen mechanism. Density functional theory computations on CO oxidation over Pd1/PTA SACs at various temperatures (100 to 700 K) were systemically examined, aiming at exploring the difference in activity of Ob and Oc atoms and the effect of temperature on CO oxidation. Based on optimized geometry, natural bond orbital, molecular orbital, Mulliken spin density, and spin population analysis of the catalyst, the Oc atom was predicted to have higher activity, which was subsequently elaborated by calculated free energy profiles of both oxygen vacancy formation paths. Moreover, a strong dependence of temperature on catalytic CO oxidation was clearly observed and even changes the rate-determining step. The computational results provide new insight into the differences in catalytic activities of surface oxygen species and the influence of temperature on the catalytic performance of CO oxidation.