A comparative study of the role of the support on the behaviour of iron based ammonia SCR catalysts

The ammonia SCR reaction has been studied using catalytic and infrared spectroscopic methods and the results compared for three different iron containing catalysts supported on an alumina, a titania and a beta zeolite. The order of SCR performance was Fe/zeolite ≫ Fe/TiO2 > Fe/Al2O3 which was in the same order as the capacity to adsorb ammonia. No evidence was found to suggest that the presence of either Brønsted or Lewis acidity is key to the activation of ammonia. NO was readily oxidised to NO2 over the Fe containing samples as indicated by the formation of nitrate even at low temperatures. The presence of water led to reduced propensity to form nitrates but did not affect the selectivity to N2O.