NO Reactions Over Ir-Based Catalysts in the Presence of O2

Abstract

The behaviour of a series of Ir-based catalysts supported on SiO₂, ZSM-5 and γ-Al2O3 with various Ir loadings prepared by impregnation method was conducted by temperature programmed reaction (TPR) technique. The result implies that NO is oxidized to NO₂ while simultaneously being reduced to N₂ or N₂O in the NO reactions over iridium catalysts. The surface active phase over iridium catalysts that promote the NO reactions is IrO₂. The catalytic activity increases with the increase of the Ir loading and support materials have a little effect on the catalytic activity. When the loading is less than 0.1%, the catalytic activity was found to be dependent on the nature of support materials and in order: Ir/ZSM-5>Ir/γ-Al₂O₃>Ir/SiO₂. When the loading is higher than 0.1%, the catalytic activity for NO oxidation is in order: Ir/ZSM-5>Ir/SiO₂>Ir/γ -Al₂O₃, which is correlated with Ir dispersion on the surface of support materials and the catalytic activity for NO reduction is in sequence: Ir/γ -Al₂O₃>Ir/SiO₂>Ir/ZSM-5, which is attributed to the adsorbed-dissociation of NO₂. Compared to Pt/γ-Al₂O₃, Ir/γ-Al₂O₃ catalyst is more benefit for the NO reduction.