Catalytic CO oxidation over palladium supported NaZSM-5 catalysts

A new Pd supported NaZSM-5 zeolite catalyst for CO oxidation at low temperature is reported. The catalyst was prepared by impregnation method. The typical 50 and 100% conversion temperatures of the catalyst (T-50 and T-100) are 38 and 90degreesC, respectively. A 2.4% Pd/NaZSM-5 catalyst can maintain its activity for CO oxidation for more than 720 h in the presence of moisture. The activities of Pd/NaZSM-5 catalysts are strongly dependent on their preparation method and pretreatment. The effects of different calcination temperature, reaction temperature, Pd loading amount and reduction atmosphere have been studied in detail. The effect of different surface Pd states on its catalytic ability has been observed. High calcination temperature results in large Pd particle dimensions, which directly leads to the decrease of activity. High reaction temperature or high Pd loading results in the high catalytic activity for CO oxidation, while H-2 reduction of catalyst causes low catalytic activity. The formation of PdO2 species on Pd/NaZSM-5 catalyst surface was strongly supported by XPS and related experiments on different treatments. Characterizations of XRD and TEM show that the surface Pd species are highly dispersed as nanoparticles over NaZSM-5 zeolite, and the dimension of particles is dependent on the pretreatment temperature. Characterization of XPS proves that small PdO2 particles are easily reduced to NO and Pd in CO or H2 atmosphere, which are related to the deactivation of the Pd/NaZSM-5 catalyst for CO oxidation. (C) 2002 Elsevier Science B.V. All rights reserved.