Selective catalytic reduction of NOx using propene and ethanol over catalysts of Ag/Al2O3 prepared by microemulsion and promotional effect of hydrogen

The present study explores the possibilities of catalysts of Ag/Al2O3, in which silver has been deposited using reverse microemulsions with the aim of getting maximum dispersion and homogeneity in the active superficial species, for the selective catalytic reduction of NOx in excess of oxygen, using both propene and ethanol as reductants and in the scope of the control of the emissions produced by vehicles that operate in conditions of lean mixture like the diesel engine or those of gasoline direct injection. The promotional effect of the hydrogen presence in the reactive mixture has also been analyzed. For both reductants, when in presence of hydrogen, an important enhancement in NOx conversion is produced, in particular for a catalyst with 3 wt.% silver. The production of acetaldehyde during the reaction employing ethanol is also analyzed and its role on the NOx reduction process has been examined. The interpretation of catalytic properties has been complemented by means of in-situ DRIFTS. (C) 2008 Elsevier B.V. All rights reserved.