The adsorption and the reaction of NH3 and NOx on supported V2O5 catalysts: effect of supporting materials

The effects of supporting materials (Al 2 O 3 , SiO 2 , TiO 2 ) on the catalytic activity and selectivity of V 2 O 5 in the reduction of NO x with ammonia are reported. The adsorbed state and the reactivity of the surface species were examined by an ir spectroscopy together with volumetric measurements, and the electronic state and the surface composition were studied by XPS.The reactivity of an adsorbed ammonia (NH 4 + ) for NO 2 over the supported catalysts was in the following increasing order, TiO 2  > Al 2 O 3  > SiO 2 . NH 4 + (ad) and NO 2 (ad) were both reactive species in the reaction over V 2 O 5 , V 2 O 5 /Al 2 O 3 , and V 2 O 5 /TiO 2 . Among these catalysts, the oxidized surface of V 2 O 5 /TiO 2 adsorbs NO as NO 2 (ad), i.e. the reactive species, whereas other catalysts did not adsorb NO unless oxygen coexisted in the gas phase. In the case of V 2 O 5 /SiO 2 , the reaction between NH 4 + (ad) and NO 2 (ad) was very slow, while the surface oxygen was easily removed by the reduction with NH 3 and resupplied by the introduction of NO on the surface. This leads to the N 2 O formation through so-called redox mechanism. The NH 4 + (ad) on V 2 O 5 /SiO 2 showed an ir absorption band at 1435 cm −1 which was much higher than those on other catalysts, and XPS measurement suggested that V 2 O 5 on SiO 2 is electrically isolated.