Enhanced redox properties of Gd-doped CeO2-TiO2 induced by oxygen vacancies and disordered structure

The redox properties of Gd-doped CeO2-TiO2 (xGd = 0.03, 0.09, and 0.15) was related to the oxygen defects and the local atomic structure. As the gadolinium doping concentration increased, a low-angle shift of the CeO2 (111) peak was observed. The EPR spectrum of the gadolinium-doped sample had an oxygen vacancy peak, indicating the oxygen vacancies induced by gadolinium. The O 1s core-level spectra showed that the ratio of oxygen vacancies gradually increased with the gadolinium doping concentration, and the Gd 4d and Ce 3d core-level spectra showed that Gd3+ reduced Ce4+ to Ce3+. An EXAFS analysis of the local atomic structures around Ce and Gd showed an increase in the Ce-O and Ce-(Ce,Gd) bond lengths and peak broadening occurred upon gadolinium doping, indicating bond dis-ordering. The same Ce-O and Gd-O bond lengths suggested that the gadolinium was substituted for the cerium site. Surface chemisorption characterization was carried out by analyzing O2-TPD and H2-TPR profiles: the peaks for oxygen desorption and hydrogen reduction gradually shifted to lower tempera-tures as the dopant concentration increased. The quantities of desorbed oxygen and reduced hydrogen also increased. These enhanced redox properties resulted from disordered Ce3+-VO**-Gd3+ acting as a surface active site, which promoted the redox reaction.(c) 2023 Published by Elsevier Ltd.