富氧条件下Ir催化NO反应

用浸渍法制备了系列Ir催化剂, 研究了富氧条件下Ir催化NO的反应, 考察了催化剂的催化反应性能及负载量和载体对催化活性的影响. 结果表明, 在Ir催化剂上不仅发生了NO氧化反应, 同时也发生了NO还原反应; Ir催化剂对NO反应有催化作用, 催化活性随Ir负载量的增加而增强. 载体对催化剂活性有一定的影响, 负载量低于0.1%(w)时, 催化NO氧化的活性顺序为Ir/ZSM-5>Ir/γ-Al2O3>Ir/SiO2, 这主要受载体自身性质的影响; 负载量高于0.1%时, 催化NO氧化的活性顺序为Ir/ZSM-5>Ir/SiO2>Ir/γ的活性顺序为Ir/γ-Al2O3>Ir/SiO2>Ir/ZSM-5, 这主要由于载体吸附作用促进了NO2在Ir催化剂上吸附分解. 与Pt催化剂相比, Ir催化剂更有利于促进NO还原.

Reaction of NO over Iridium Catalysts with Excess Oxygen

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.