Diesel soot combustion on Mo/Al2O3 and V/Al2O3 catalysts: investigation of the active catalytic species

We studied the reactivity of Mo/Al2O3 and V/Al2O3 catalysts for soot combustion, and the influence of their volatile (MoO3 and V2O5) and superficial dispersed species. Differential exploratory calorimetry and temperature-programmed oxidation (TPO) experiments with catalyst and soot mixtures showed that lower combustion temperatures were obtained with increasing loading of Mo or V. TPO experiments performed on separate layers of soot and catalyst showed that both species were able to oxidize CO to CO2, but the combustion temperature was lowered only when soot was in contact with the dispersed species. Infrared absorption spectroscopy analyses of CO adsorbed at several temperatures showed that all catalysts formed superficial carbonated species; however, on molybdenum catalysts, they were easily decomposed. Therefore, it is suggested that the reaction occurs by formation of carbonate species at the catalyst/soot interface yielding CO2, and the better performance of molybdenum catalysts is due to the higher instability of carbonated species.