The effect of existence states of PdOx supported by Co3O4 nanoplatelets on catalytic oxidation of methane

Abstract

Abstract Three types of nanoplatelet-like Co3O4-supported Pd catalysts were prepared to investigate the effect of existence states of Pd species on catalytic combustion of methane. The Pd-Co3O4 catalysts performed the best performance for CH4 combustion than Pd/Co3O4 and Pd@Co3O4, with much higher catalytic activity (T90:337\xa0°C vs. 361\xa0°C and 372\xa0°C) and lower apparent activation energy (Ea: 66.9\xa0kJ\xa0mol−1 vs. 89.7\xa0kJ\xa0mol−1 and 90.5\xa0kJ\xa0mol−1). Besides, the Pd-Co3O4 catalysts exhibited excellent resistance ability of co-existence with H2O and CO2 poisoning. Experimental observations suggested that the Pd-Co3O4 possessed the highest Pd dispersion, thus exposing the largest amount of surface active PdO species among these catalysts. Furthermore, embedded Pd-Co3O4 architecture endowed more active adsorbed oxygen species and abundant oxygen vacancies, and better reducibility. More importantly, combined with O2-TPD, H2-TPR, CH4-TPSR, and quasi in situ XPS observations, it was also evidenced that the surface adsorbed oxygen species were defined as primary active oxygen species. These reactive oxygen species were consumed by methane oxidation and regenerated via adsorption and activation of gaseous oxygen on surface oxygen vacancies and transformation from lattice oxygen. Our work here paves the pathway for rational design of high-performance Pd-based catalysts in hydrocarbon oxidation.