Evolution of Ce4+ Lewis acidity during dehydroxylation of ceria nanoparticles with different morphology: An integrated FTIR, DFT and HRTEM study
Kristina Chakarova, Videlina R. Zdravkova, Bayan S. Karapenchev, D. Nihtianova, Elena Ivanova, Hristiyan A. Aleksandrov, Iskra Z. Koleva, D. Panayotov, Mihail Mihaylov, Georgi N. Vayssilov, Konstantin Hadjiivanov
Abstract
Ceria is an important redox catalyst and its activity depends on the open Ce4+/Ce3+ sites, anion vacancies, surface OH groups and the ratio between them. We investigated the effect of dehydroxylation on the evolution of Ce4+ Lewis acidity of oxidized ceria nanocubes, nanopolyhedra, and nanorods. The {1 1 1} face is not hydroxylated and the exposed Ce4+ sites, after dehydration, adsorb CO weakly, forming linear carbonyls. The hydroxyl coverage of the {1 1 0} face consists of terminal and bridging hydroxyls, and dehydroxylation occurs between 423 and to 573 K by interaction between these groups. The produced Ce4+ sites form stronger linear carbonyls. The {1 0 0} face is covered by bridging OH groups, which are progressively removed even at 773 K. The created Ce4+ sites coordinate CO in a bridging mode and, at higher coverage, connect two bridging CO molecules. Ce4+ sites on edges and defects appear at high evacuation temperature and form mono- and dicarbonyls.