Abstract: A series of iridium-supported catalysts with various Ir loadings were prepared by impregnation method. The support materials used were ZSM-5, γ-Al2O3, and SiO2. The Ir loadings examined were 0.02%, 0.1%, 1%, and 5% (w). The behavior of the catalysts for the NO reaction was analyzed by means of temperature programmed reaction (TPR) experiments. The reactions of NO over iridium include the oxidation of NO to NO2 and the reduction of NO to N2 or N2O. The iridium catalysts promote the reactions of NO and the catalytic activity increases with the increase of the Ir loadings. Further, support materials have a little effect on the catalytic activity. When the loading was less than 0.1%, the catalytic activity was found to be dependent on the property of support materials and the activity order was Ir/ZSM-5>Ir/γ-Al2O3>Ir/SiO2; when the loading was higher than 0.1%, the order of catalytic activity for NO oxidation was Ir/ZSM-5>Ir/SiO2>Ir/γ-Al2O3, which was correlated with Ir dispersion on the surface of support materials, and the order of catalytic activity for NO reduction was Ir/γ-Al2O3>Ir/SiO2>Ir/ZSM-5, which was attributed to the adsorbed-dissociation of NO2. Ir/γ-Al2O3 catalyst was more beneficial for the NO reduction than Pt/γ-Al2O3 catalyst.

Key words: Excess oxygen, Ir catalyst, NO oxidation, NO reduction