Engineering surface and subsurface oxygen vacancies of CeZrO solid solution for enhanced total toluene oxidation.

Most studies have shown that oxygen vacancies on CeZrO solid solution are important for enhancing the catalytic oxidation performance. However, a handful of studies investigated the different roles of surface and subsurface oxygen vacancies on the performance and mechanisms of catalysts. Herein, a series of zirconium doping on CeO samples (CeO, CeZrO, and CeZrO) with various surface-to-subsurface oxygen vacancies ratios have been synthesized and applied in toluene catalytic oxidation. The obtained CeZrO exhibits an excellent catalytic performance with a 90 % toluene conversion at 295 °C, which is 68 °C lower than that of CeO. Additionally, the obtained CeZrO catalyst also exhibited good catalytic stability and water resistance. The XRD and HRTEM results show that Zr ions are incorporated into CeO lattice, forming CeZrO solid solution. Temperature-programmed experiments reveal that CeZrO shows excellent low-temperature reducibility and abundant surface oxygen species. In-situ DRIFTS tests were used to probe the reaction mechanism, and the function of Zr doping in promoting the activation of oxygen was further determined. Density functional theory (DFT) calculations indicate that the vacancy formation energy and O adsorption energy are both lower on CeZrO, confirming the reason for its superior catalytic performance.