Catalysts of self-assembled Pt@CeO_2−δ-rich core–shell nanoparticles on 3D ordered macroporous Ce_1−xZr_xO₂for soot oxidation: nanostructure-dependent catalytic activity

Abstract

The catalytic performance in heterogeneous catalytic reactions consisting of solid reactants is strongly dependent on the nanostructure of the catalysts. Metal-oxides core-shell (MOCS) nanostructures have potential to enhance the catalytic activity for soot oxidation reactions as a result of optimizing the density of active sites located at the metal-oxide interface. Here, we report a facile strategy for fabricating nanocatalysts with self-assembled Pt@CeO_2-δ-rich core-shell nanoparticles (NPs) supported on three-dimensionally ordered macroporous (3DOM) Ce_1-xZr_xO₂via the in situ colloidal crystal template (CCT) method. The nanostructure-dependent activity of the catalysts for soot oxidation were investigated by means of SEM, TEM, H₂-TPR, XPS, O₂-isothermal chemisorption, soot-TPO and so on. A CeO_2-δ-rich shell on a Pt core is preferentially separated from Ce_1-xZr_xO₂ precursors and could self-assemble to form MOCS nanostructures. 3DOM structures can enhance the contact efficiency between catalysts and solid reactants (soot). Pt@CeO_2-δ-rich core-shell nanostructures can optimize the density of oxygen vacancies (O_v) as active sites located at the interface of Pt-Ce_1-xZr_xO₂. Remarkably, 3DOM Pt@CeO_2-δ-rich/Ce_1-xZr_xO₂ catalysts show super catalytic performance and strongly nanostructure-dependent activity for soot oxidation in the absence of NO and NO₂. For example, the T₅₀ of the 3DOM Pt@CeO_2-δ-rich/Ce_0.8Zr_0.2O₂ catalyst is lowered down to 408 °C, and the reaction rate of the 3DOM Pt@CeO_2-δ-rich/Ce_0.2Zr_0.8O₂ catalyst (0.12 μmol g^-1 s^-1) at 300 °C is 4 times that of the 3DOM Pt/Ce_0.2Zr_0.8O₂ catalyst (0.03 μmol g^-1 s^-1). The structures of 3DOM Ce_1-xZr_xO₂-supported Pt@CeO_2-δ-rich core-shell NPs are decent systems for deep oxidation of solid reactants or macromolecules, and this facile technique for synthesizing catalysts has potential to be applied to other element compositions.