Kinetics of the selective catalytic reduction of nitrogen oxide (NO) with ammonia over manganese oxide (Mn2O3)-tungsten oxide (WO3)/.gamma.-alumina

Abstract

A kinetic study of the selective catalytic reduction (SCR) of NO with NH[sub 3] over an alumina-supported Mn[sub 2]O[sub 3]-WO[sub 3] (10.8 wt % Mn[sub 2]O[sub 3], 6.8 wt % WO[sub 3]) catalyst has been conducted between 383 and 423 K at atmospheric pressure over a broad range of concentration conditions (100-2,000 ppm NO and NH[sub 3], 0.5-10% O[sub 2]) and space times (W/F[sub NO] = 220-17,647 kg[center dot]s/mol). A kinetic model is proposed on the basis of mechanistic insights in the SCR process and data on manganese oxide catalysts, using two different types of sites: one for NH[sub 3] adsorption and the other for NO and O[sub 2] adsorption. The selected rate expression, derived from this model, can describe the entire data set within 3% conversion accuracy. A Freundlich type of NO adsorption had to be assumed. At the intermediate temperatures the rate expression reduces to a power rate expression which describes the results equally well. The apparent reaction order is over the range of conditions approximately 0.4 to NO and O[sub 2] and around 0 for NH[sub 3]. The overall activation energy amounts to 20-30 kJ/mol.