γ-Al2O3 supported Pd@CeO2 core@shell nanospheres: salting-out assisted growth and self-assembly, and their catalytic performance in CO oxidation

Abstract

In this paper, we have successfully demonstrated the clean synthesis of high-quality Pd@CeO₂ core@shell nanospheres with tunable Pd core sizes in water, and furthermore loaded the as-obtained Pd@CeO₂ products on commercial γ-Al₂O₃via electrostatic interaction. KBr here plays two key roles in inducing the growth and self-assembly of Pd@CeO₂ core@shell nanospheres. First, Br⁻ ions can retard the reduction of Pd²⁺ ions via the formation of the more stable complex of [PdBr₄]²⁻ so as to tune the size of Pd cores. Second, it greatly decreases the colloidal stability, and hence the surface polarity-weakened Pd and CeO₂ NPs have to spontaneously self-assemble into more stable and ordered structures. Among different-sized Pd samples, the as-obtained 8 nm-Pd@CeO₂/Al₂O₃ one exhibits the best performance in catalytic CO oxidation, which can catalyze 100% CO conversion into CO₂ at 95 °C, which is much lower than the previously reported CeO₂-encapsulated Pd samples.