CATALYTIC COMBUSTION OF DIESEL SOOT OVER METAL-OXIDE CATALYSTS

The activity of different metal oxides in the catalytic combustion of a diesel soot having a high amount of adsorbed hydrocarbons has been i nvestigated and tested in a TPO apparatus. Two different steps have be en observed. The first is related to the combustion of hydrocarbons ad sorbed on soot and the second one to the combustion of the graphitic s olid fraction. A high surface area Fe2O3 was found to be the most acti ve catalyst for the oxidation of hydrocarbons, whereas V2O5 was also a ble to promote the combustion of graphitic carbon. The oxidation of th e hydrocarbon fraction has been correlated with the surface area and t he strength of the metal-oxygen bond of the metal oxide. The combustio n of graphitic carbon is favoured instead on metal oxides having a low melting point. The effect of platinum addition to gamma-alumina has b een also investigated. Spillover of activated oxygen from Pt to the su pport has been postulated to take into account the promotion of the ox idation of graphitic carbon.