Catalytic properties of Cn on sulphated zirconias for DeNOx in excess of oxygen using n-decane as reductant

The selective catalytic removal of NO by decane, in oxygen rich atmosphere has been investigated on Cu/sulphated zirconia catalysts. The introduction of Cu using Cu(acac)(2) in organic solvent results in well dispersed CU2+ and little change of acidity of the carrier. In absence of sulphate on the support a linear correlation between catalytic activity and the reducibility of Cu ions can be obtained from previous results. By contrast, for Cu/SZ catalysts, DeNO(x) obeys a bifunctional mechanism. The activity per exposed Cu atom is constant at low temperature whatever the acidity of the support, showing that the rate determining step is then controlled by copper. Above 600 K the turnover frequency increases with the amount of sulphur on the support, showing that the slow step is now an acid catalysed reaction. Water has only a reversible effect on activity. The largest inhibition is due to SO2: adding 20 ppm of SO2 to the feed results in a fourfold decrease of rate. This inhibition is sensitive to the dispersion of Cu: poorly dispersed catalyst obtained by impregnation, are not inhibited by sulphur dioxide, and a compromise must then be found between activity and thioresistance. (C) 1998 Elsevier Science B.V. All rights reserved.