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

A series of Cu-Mn mixed oxides were prepared via a facile co-precipitation method and used as catalysts for diesel soot combustion in NOx/O-2/N-2. 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 Cu1.5Mn1.5O4 was obtained (named Cu1Mn1), which exhibited superior catalytic activity (e.g., finishing combustion temperature (T-f) = 360 degrees 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 O-2, NO and NO2; and (2) the high intrinsic activity of the Cu1.5Mn1.5O4 phase: the abundant adsorbed oxygen species (O-ads) is beneficial to the direct oxidation of soot into CO2, and the enormous Cu+-Mn lambda+ (lambda = 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.