Enhancement of the visible-light photocatalytic activity of CeO2 by chemisorbed oxygen in the selective oxidation of benzyl alcohol

To afford high efficient catalytic oxidation alcohols activity, enhancement of the visible light photocatalytic activity of CeO2 have attracted great attention. On the photocatalytic oxidation of alcohols, the chemisorbed oxygen on the CeO2 nanostructure play an important promoter role. The deep understand on the formation and the detail roles of chemisorbed oxygen on the CeO2 nanostructure are therefore highly desirable. In this work, we successfully obtained the CeO2 photocatalysts that provide different concentrations of chemisorbed oxygen through hydrolyzing Ce(NO3)3 in the saturated atmosphere of Ar, air, and O2 (denoted as CeO2-Ar, CeO2-Air, and CeO2-O2, respectively). The visible light (≥400 nm) photocatalytic performance of CeO2-O2 photocatalysts (~100 % selectivity and conversion) in the selective oxidation of benzyl alcohol was enhanced by a factor of 1.54 and 1.43 as compared to CeO2-Ar and CeO2-Air respectively, owing to their varying concentrations of chemisorbed oxygen on CeO2-Ar, CeO2-Air, and CeO2-O2 photocatalysts. Based on our detail characterizations relative to the chemisorbed oxygen, the enhancement mechanism of chemisorbed oxygen was proposed for CeO2 photocatalysts: First, the O2 molecules were chemisorbed on Ce(III) sites, forming a Ce peroxo structure, which was beneficial to the harvesting visible light for CeO2 photocatalysts. Whereafter, this Ce peroxo structure can easily capture the photoexcited electrons, resulting in the O2•− which collaboratively activate the photocatalytic oxidation reaction with holes. Furthermore, the Ce(III) defects sites will chemisorb oxygen involved in the reaction system to produce the ceria peroxo structure again. Such recycle procedure will undoubtedly increase the utilization efficiency of chemisorbed oxygen and thus enhanced the visible light photocatalytic activity of CeO2.