Synergetic Effect of K Sites and Pt Nanoclusters in an Ordered Hierarchical Porous Pt-KMnO_<i>x</i>/Ce_0.25Zr_0.75O₂ Catalyst for Boosting Soot Oxidation

Abstract

We have designed and elaborately fabricated the ordered hierarchical macro-meso-microporous catalysts of Ce0.25Zr0.75O2-supported Pt-embedded KMnOx nanoparticles (OMMM Pt-KMnOx/Ce0.25Zr0.75O2). Three dimensionally ordered macro-mesoporous (3DOMM) Ce0.25Zr0.75O2 oxide was synthesized by the combined methods of evaporation-induced interfacial self-assembly (EISA) and colloidal crystal templates (CCT). KMnOx nanoparticles (NPs) possess the natural microporous nanostructure of an octahedral molecular sieve (OMS) with an average size of 0.46 nm. Pt nanoclusters were anchored in situ at the microporous structure of KMnOx NPs and formed Pt-KMnOx active sites. For the OMMM Pt-KMnOx/Ce0.25Zr0.75O2 catalyst, a 3D ordered macroporous (250 nm) structure can enhance contact efficiency between soot and catalysts, and a high specific surface area with contributions from ordered mesopores (5 nm) is beneficial for dispersion of KMnOx NPs and activation of gaseous reactants (O2 and NO). Meanwhile, a microporous (0.46 nm) structure can anchor K sites and ultrafine Pt nanoclusters. The synergetic effect of ternary K-Mn-Pt components can transform gas reactants to the effective intermediate species and thereafter oxidize the well-dispersed soot particles. The OMMM Pt-KMnOx/Ce0.25Zr0.75O2 catalyst possesses high catalytic activity and stability for soot oxidation under the conditions of loose contact: i.e., its TOF value is 2.10 h–1 at 290 °C, which is more than a 4-fold increase over the 3DOMM Ce0.25Zr0.75O2 support (0.47 h–1). The architected hierarchical porous structure rationalizes an alternative protocol to improve solid–solid contact and the resulting activity, which can be further applied to other catalysis systems with different catalysts and reactants.