Reactivity in the removal of SO2 and NOx on Co/Mg/Al mixed oxides derived from hydrotalcites

Metal containing hydrotalcites, where metal oxides present redox properties and hydrotalcite shows a basic character, appear to be new important envir onmental catalysts for the removal of SOx and NOx. Redox and basic properti es 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 ch aracterized showing that cobalt is present in two forms, as isolated and we ll dispersed paramagnetic ions, and as very small Co-containing particles ( in the nanometric range), with an internal antiferromagnetic ordering at lo w temperature. The redox properties of cobalt allow the reduction of NO wit h propane at high temperatures and in presence of oxygen. The reduced cobal t species are proposed as the active sites. Nevertheless, for the removal o f SO2 and contrary to the case of Cu/Mg/Al samples, the addition of an oxid ant as cerium oxide on Co/Mg/Al is necessary in order to oxidize SO2 to SO3 . In this case, similar results than those obtained with previously reporte d catalyst, i.e. cerium or copper-cerium hydrotalcite, are obtained. These results indicate that this catalyst could be an adequate material for the s imultaneous removal of SO2 and NOx in a FCC unit. (C) 1999 Elsevier Science B.V. All rights reserved.