Pt-free CoAl2O4 catalyst for soot combustion with NOx/O2

Cobalt aluminate spinel compounds prepared by different methods were characterized in terms of crystalline structure, morphology, textural properties and acidity, and evaluated as catalysts for diesel soot combustion in NOx/O-2 mixtures. The activation of commercial CoAl2O4 microparticles by ball milling reduced the onset temperature of this material considerably and yielded an efficient catalyst for soot combustion that exhibited a temperature of half conversion, 411 degrees C, similar to that obtained with the reference Pt/Al2O3 catalyst. Moreover, like Pt, the milled CoAl2O4 suppressed the CO formation observed in non-catalytic soot combustion. The significant modification of the particle size, the emergence of new exposed crystal facets and the creation of defects are responsible for the appearance of new active sites and high acidity that improved catalyst-to -soot contact and reactivity. The findings open a new gate toward the use of efficient Pt-free catalyst for soot combustion.