Influence of hydrothermal synthesis conditions on lattice defects in cerium oxide

Abstract

Cerium oxide makes one of the most promising materials for chemical transformations in environmental and energy applications. Herein, the influence of hydrothermal conditions on the physico-chemical characteristics of cerium oxide prepared from salt solution via ammonia precipitation is analyzed. The systems are well characterized using SEM, TEM, XRD analysis, photoluminescence spectra, Raman spectra, TPR study. and XPS analysis. Normal aqueous conditions lead to particles of size ~8 ​nm, with truncated octahedral geometry, closer to spheroid shape (RT-Ce) bound by {111} and {100} planes. Elevated temperature facilitated preferential exposed {100} plane bounded cubic ceria structures of size ~15 ​nm (HT-Ce), which are stabilized by more number of anion vacancies. Low temperature synthesis yielded smaller sized particles with less crystallinity and higher surface area, when compared to hydrothermal route. Lattice defects, represented in terms of Ce3+ ions and associated lattice oxygen vacancies are seen in higher amounts in ceria synthesised via hydrothermal path, as supported by various characterization results. CeO2 achieved via hydrothermal path exhibited higher catalytic oxidation activity, which is examined using a model oxidation reaction, vis., CO oxidation. The enhanced activity of HT-Ce is explained through the defect structure induced facile redox shift in the system.