Monolithic FeO x /Al2O3 catalysts for ammonia oxidation and nitrous oxide decomposition

Abstract

(1.2–8.3)%FeOх/Al2O3 monolith catalysts have been prepared by impregnating alumina with aqueous solutions of iron(III) nitrate and oxalate and have been tested in NH3 oxidation and in the selective decomposition of N2O in mixtures resulting from ammonia oxidation over a Pt–Rh gauze pack under conditions of nitric acid synthesis (800–900°C). In the case of the support calcined at 1200°C, the catalyst is dominated by bulk Fe2O3 particles localized on the Al2O3 surface. The activity of these samples in both reactions decreases with a decreasing active component content, thus limiting the potential of Fe2(C2O4)3 · 5H2O, an environmentally friendlier but poorly soluble compound, as a substitute for Fe(NO3)3 · 9H2O. Decreasing the support calcination temperature to 1000°C or below leads to the formation of a highly defective Fe–Al–O solid solution in the (1.2–2.7)%FeOх/Al2O3 catalysts. The surface layers of the solid solution are enriched with iron ions or stabilize ultrafine FeOх particles. The catalytic activity of these samples in both reactions is close to the activities measured for ~8%FeOх/Al2O3 samples prepared using iron nitrate.