Migration roles of different oxygen species over Cu/CeO2 for propane and soot combustion

Abstract

Determining the migration rules of oxygen species in catalytic combustion, especially for catalysts composed of transition metal oxides, is essential yet challenging. This study hydrothermally synthesized nanosphere-structured cerium dioxide (CeO2) and its copper-loaded catalysts (Cu/CeO2) to identify the distinct functions of superficial oxygen species (O) and lattice oxygen (O2–). The presence of Cu-Ce solid solution at the Cu/CeO2 interface lowered the apparent activation energy for the catalytic combustion of propane and soot. The catalytic combustion of propane followed the Mars-van Krevelen mechanism, with O2– serving as the dominant reactive phase while O played a subordinate role. The solid–solid reaction between soot and superficial oxygen of the catalyst was responsible for catalyzed soot combustion. The O species produced by surface defective sites exhibited higher activity than O2–, which drained easily at the beginning of the reactions. The isotopic oxygen exchange tests revealed the mechanism of metal oxide (CuO/CeO2) interactions for active oxygen species migration, with the results demonstrating the solid solution at the phase interface as portholes for oxygen migration, thus increasing oxygen mobility between the gaseous phase and the surface by lowering the migration activation energy. In situ, infrared results showed that the reaction path of soot catalytic combustion was single, without any intermediate production formation, compared to multiple paths in the propane oxidation process. This study provided an easily implemented and widely applicable method, which deepens our understanding of the characterization of the function and migration of predominant oxygen species in diverse combustion reactions involving oxide-based catalysts. Additionally, this study clarified differences and similarities between the reaction mechanisms of solid–solid and solid–gas catalysis.