Facile synthesis of spinel Cu1.5Mn1.5O4 microspheres with high activity for the catalytic combustion of diesel soot

Abstract

A series of Cu–Mn mixed oxides were prepared via a facile co-precipitation method and used as catalysts for diesel soot combustion in NO_x/O₂/N₂. It is found that the chemical composition in the Cu–Mn mixed oxides has a significant influence on both morphology and catalytic activity. When the Cu/Mn atomic ratio was optimized to be 1, a distinctive pure spinel phase of Cu_1.5Mn_1.5O₄ was obtained (named Cu1Mn1), which exhibited superior catalytic activity (e.g., finishing combustion temperature (T_f) = 360 °C, in loose contact mode). The excellent catalytic activity of Cu1Mn1 was mainly attributed to the following aspects: (1) distinct morphological features: the well-dispersed Cu1Mn1 microspheres with a rough surface could contact soot particles sufficiently, and the stacked pores between the loosely packed nanoparticles within the microspheres could facilitate the diffusion of gaseous O₂, NO and NO₂; and (2) the high intrinsic activity of the Cu_1.5Mn_1.5O₄ phase: the abundant adsorbed oxygen species (O_ads) is beneficial to the direct oxidation of soot into CO₂, and the enormous Cu⁺–Mn^λ+ (λ = 3, 4, hereinafter inclusive) cation pairs could facilitate the production of the strong oxidant NO₂, and the interaction between Cu²⁺ and NO₂ would lead to high enhancement efficiency of NO₂ for soot combustion. This facile strategy for the high activity spinel phase towards catalytic soot combustion shows great promise for practical applications.