Reactivity in the removal of SO_2 and NO_x on Co/Mg/Al mixed oxides derived from hydrotalcites

摘要

Metal containing hydrotalcites, where metal oxides present redox properties and hydrotalcite shows a basic character, appear to be new important environmental catalysts for the removal of SO_x and NO_x. Redox and basic properties of a mixed Co/Mg/Al oxide derived from hydrotalcites are tuned in order to achieve the optimal catalytic behavior required. This sample has been characterized showing that cobalt is present in two forms, as isolated and well dispersed paramagnetic ions, and as very small C0-containing particles (in the nanometric range), with an internal antiferromagnetic ordering at low temperature. The redox properties of cobalt allow the reduction of NO with propane at high temperatures and in presence of oxygen. The reduced cobalt species are proposed as the active sites. Nevertheless, for the removal of SO_2 and contrary to the case of Cu/Mg/Al samples, the addition of an oxidant as cerium oxide on Co/Mg/Al is necessary in order to oxidize SO_2 to SO_3. In this case, similar results than those obtained with previously reported catalyst, i. e. cerium or copper-cerium hydrotalcite, are obtained. These results indicate that this catalyst could be an adequate material for the simultaneous removal of SO_2 and NO_x in a FCC unit.