Roles of Surface-Active Oxygen Species on 3DOM Cobalt-Based Spinel Catalysts MxCo3–xO4 (M = Zn and Ni) for NOx-Assisted Soot Oxidation

Abstract

Co3O4 is a well-known catalyst in the oxidation reaction. In such a catalyst, the geometric and electronic structures of tetrahedrally coordinated Co2+ and octahedrally coordinated Co3+ can be regulated by directional metal ion substitution strategy, accompanied by the modification of catalytic activity. Herein, normal and inverse cobalt-based spinel catalysts MxCo3–xO4 (M = Zn and Ni) with a three-dimensionally ordered macroporous (3DOM) structure were successfully fabricated through the carboxy-modified colloidal crystal templating (CMCCT) method. The relationship between the dopant and activity during NOx-assisted soot oxidation was systematically studied by means of XPS, H2-TPR, soot-TPR, isothermal anaerobic titrations, NO-TPO, soot-TPO, and so on. The well-defined 3DOM structure for MxCo3–xO4 catalysts can improve the contact efficiency of soot and catalysts. 3DOM NiCo2O4 exhibits high catalytic activity for soot oxidation under a loose contact mode between soot and catalyst. For instance, its T50 a...