The contributions of distinct Pd surface sites in palladium–ceria catalysts to low-temperature CO oxidation

Abstract

Palladium-loaded catalysts exhibit promising low-temperature catalytic activity toward CO oxidation. In this work, ceria with well-defined facets was utilized as a support to investigate the structure evolution of palladium species and, thereby, the correlation of this with the catalytic properties. A typical relationship between the distribution of palladium species and the Pd content and calcination conditions has been detected. Calcinating under an O₂ atmosphere results in three different Pd species: PdO_x aggregates, PdO nanoparticles, and Pd–O–Ce solid solution. The results show that high palladium-loading facilitates the enrichment of Pd in PdO_x and PdO forms, while low palladium-loading induces the dissolution of considerable amounts of Pd into the bulk to form Pd–O–Ce. Further structural evolution resulting from the decomposition of PdO_x to Pd–O–Ce has been detected during the calcination process under a CO atmosphere. Furthermore, it is found that calcinating in synthetic gas (a mixture of CO and O₂) stimulates the regeneration of decomposed palladium species on the surface. In correlation with the structure evolution, PdO_x and PdO species are essential for improving the low-temperature catalytic properties.