Fabrication of Spinel-Type Pd_<i>x</i>Co_3–<i>x</i>O₄ Binary Active Sites on 3D Ordered Meso-macroporous Ce-Zr-O₂ with Enhanced Activity for Catalytic Soot Oxidation

Abstract

3D ordered meso-macroporous (3DOMM) Ce0.2Zr0.8O2 (CZO) was successfully synthesized by a combined method of evaporation-induced interfacial self-assembly (EISA) and colloidal crystal templates (CCT). The multifunctional catalysts of spinel-type PdxCo3–xO4 nanoparticles (NPs) supported on 3DOMM CZO were fabricated by a gas bubbling assisted coprecipitation (GBCP) method. The relationship between nanostructure (hierarchical pore and spinel-type active phase) and activity during catalytic soot oxidation was studied by the techniques of SEM, TEM, XPS, H2-TPR, NO oxidation, soot-TPO, and so on. The 3DOMM structure with a larger surface area and total pore volume increases the amount of supported active sites and enhances the contact efficiency between reactants (soot, O2, and NO) and catalysts. Spinel-type PdxCo3–xO4 (AB2O4) binary active sites by substitution for Co2+ (A site) with Pd2+ cations are beneficial for improving activation efficiency for gaseous reactants (NO and O2). The novel nanocatalysts of 3DOMM CZO-supported spinel-type PdxCo3–xO4 NPs exhibited superb catalytic performance and strong nanostructure-dependent activity for soot oxidation under loose contact of soot with catalyst. For instance, the T10, T50, and T90 values of 3DOMM PdCo2O4/CZO catalyst with the highest catalytic activity (TOF = 2.56 h–1) are only 313, 367, and 404 °C, respectively. The NO2-assisted catalytic mechanism for soot oxidation is studied and proposed by in situ Raman spectra, and the role of spinel-type PdCo2O4 binary active sites is revealed. 3DOMM PdxCo3–xO4/CZO catalysts are decent systems for soot oxidation, and the easy preparation technology has the potential for application to catalysts with other element compositions.