Role of acidic sites in the de-NOx process on supported tin oxides

The influence of the acidic properties of the support on the catalytic performances of supported SnO2 surfaces has been investigated. The acidic properties of low Sn loading catalysts (ca. 3 wt.%) prepared starting from ShCl4, 5 H2O precursor and supported on γ-Al2O3, MgO, SiO2, TiO2, and ZrO2 were characterized by ammonia adsorption microcalorimetry. The catalysts were tested in the NO reduction with ethylene under high oxygen partial pressure at very high space velocity (50.000 h-1). The catalysts prepared on the acidic supports (ZrO2, Al2O3 and TiO2) were the most active. For Sn-ZrO2 at 425°C, 47% conversion of 5000 ppm NO to N2 and 77% conversion of 5000 ppm of C2H4 to CO2 were obtained in presence of 9% O2. Based on the N2 yield, the following scale of activity was found: Sn-ZrO2 > Sn-TiO2 ≈ Sn-Al2O3 >> Sn-SiO2.