Influence of the calcination temperature on the structure and reducibility of nanoceria obtained from crystalline Ce(OH)CO_3 precursor

摘要

A high yield green method was developed for the preparation of reactive nanotextured ceria (CeO_2). The preparation method is based on the oxidation of a crystalline Ce(OH)CO_3 precursor that decompose at relative low temperature (ca. 250 ℃) yielding CeO_2 nano-crystals initially rich in Ce~(3+). After increasing calcination temperatures (in the range 350-650 ℃), PXRD analysis show a slight crystal growth after calcination temperatures up to 550 ℃, however cell contraction in such case denotes the definitive oxidation of remnant Ce~(3+) centers. XPS results confirm Ce~3+ fraction diminution as calcination temperature increases. TPR profiles of ceria samples show two reduction events being the low temperature one (at ca. 500 ℃) related to a surface process in which approximately only one cerium monolayer is involved. Catalytic activity tests for COPROX reaction were performed under differential reactor conditions to evaluate their activity in the temperature range 100-300 ℃. The optimum activity recorded for the sample calcined at 450 ℃ accounts for the compromise between oxide's activation and surface preservation.