Influence of the Acidic Properties of ZrO2 Based Mixed Oxides Catalysts in the Selective Reduction of NOx with n-Decane

The selective catalytic reduction of NOx by decane (C10H22-SCR) has been studied over mixed oxides of zirconia with boria, alumina, gallia, india and tungsta. The samples were prepared by coprecipitation and thoroughly characterized using a combination of different techniques to determine their structural and surface properties. Moreover a WO3-containing sample supported on Al2O3-ZrO2 sample was prepared to verify the influence of the tungsta active phase deposited by impregnation. The surface acidity and basicity of the samples (measured by NH3 and SO2 adsorption microcalorimetry) varied in relation to the kind of co-oxide added to zirconia. In particular, the number of surface acid sites expressed in mu g(-1) increased in the following order WO3-ZrO2 > Al2O3-ZrO2 > Ga2O3-ZrO2 > In2O3-ZrO2 > WO3/(Al2O3-ZrO2) > ZrO2 > B2O3-ZrO2. Correlations between the catalytic behaviour and the samples surface acidity were found and the results show that a moderate acidity (i.e. for Ga2O3-ZrO2) is one of the key parameter for high N-2 selectivity and NOx conversion.