| Abstract: | Zeolites containing transition metal ions were investigated with regard to their physical and chemical properties. The samples of MnY, FeY, CrY, CrX and CrA were prepared by aqueous ion exchange methods. Subsequent pretreatment procedures produced zeolite solids with diverse chemical and physical properties. Hydrated MnY zeolites were found to be catalytically active in the oxidation of SO2 to form a strongly bound surface SO4[^-2] product. This product was detected both by gravimetric adsorption and direct chemical analysis. Dehydration of the MnY resulted in the loss of catalytic activity. It was determined that this was due to the removal of all zeolitic water which is a reactant in the production of SO4[^-2]. Despite severe interference by a Knudsen diffusion process, the oxidation reaction was determined to be first order with respect to SO2. MnY and FeY zeolites were investigated using powder x-ray diffractometry to determine the distribution and coordination of cations after various pretreatments. The Mn(II), Fe(II) and Fe(III) cations all demonstrated a preference for site I occupancy after dehydration. Occupancy of other sites depended on a number of factors and no generalizations are available. The distribution of cations in these samples was also found to be influenced by prolonged x-irradiation. During this irradiation, a major cationic redistribution was noted and accompanied by the formation of novel bridged complexes inside the sodalite cages. Zeolites containing chromium were studied using a number of chemical and instrumental techniques which included the use of nitric oxide as a probe molecule. In addition, a method was developed whereby the epr parameters of model molecules could be determined from molecular orbital calculations. It was found that Cr remains in the trivalent state after dehydration in CrY zeolites. The addition of nitric oxide to these samples resulted in the formation of dinitrosyl complexes of Cr(III). In CrX lattices, however, the presence of some Cr(II) was thought to be possible after similar pretreatments. Dehydrated CrA zeolites did not form nitric oxide adducts. The reason for this was thought to lie in the relative instability of A-type lattices. This instability also gave rise to the formation of bridged complexes in which the Cr(V) ion was linked to an Al(III) ion via an oxide bridge. The aluminum and oxygen were both postulated to be from the zeolitic lattice itself. |
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