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Physical and Catalytic Properties of the Na-exchanged Y-Zeolites with different Si/Al ratios

机译：Physical and Catalytic Properties of the Na-exchanged Y-Zeolites with different Si/Al ratios

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A series of sodium-exchanged Y-zeolites with different Si/Al ratios have been prepared from the proton and ammonium ion forms of Y-zeolite(faujasite) by means of a solution ion exchange. The prepared catalysts have been characterized by the various analytical techniques and the NOx conversion rates of the catalysts were measured with a non-thermal plasma assisted catalytic system. Specific surface areas measured by the BET increased in the order of the NaY series 780, 712, 100, 720, 760. The results of the elemental analyses showed that the Si/Al ratio of the catalysts increased gradually in the order of NaY 100, NaY 712, NaY 720, NaY 760, NaY 780. The comparison of the bulk and surface compositions indicated that the Al content on the surface was larger than that of the bulk. XRD results showed that the crystalline structures of the processed zeolites were the same as that of the zeolite Y, even when the Si/Al ratios were different. The magnitude of the lattice parameters was proportional to the results of the NOx reduction measurements, except for the case of NaY 780, in all the zeolites. TGA results showed that the amount of desorbed water gradually increased, as the ratio of the Si/Al decreased, and these results agreed with the results of the NOx conversion measurements. FTIR spectra of the CO_2 adsorbed on to the catalyst surfaces showed two adsorption sites, but the chemical shifts for the different Si/Al ratios were not observed. The trend for the amount of CO_2 adsorbed on to the catalysts agreed with the results of the NOx conversion measurements. The NOx conversion rates measured by the non-thermal plasma technique increased in the order of NaY 780, NaY 760, NaY 720, NaY 712, NaY 100, which is reversely proportional to the ratio of the Si/Al of the catalysts. These results indicated that the major factor influencing the catalytic activities of the zeolitic catalysts in terms of the NOx reduction was, primarily the Si/Al ratio of the bulk phase of the zeolites, and secondly the ratio of the Si/Al composing the surface of the zeolites.

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