Exafs Studies of Transition Metal Exchanged Zeolites

172 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.The extended X-ray absorption fine structure (EXAFS) that appears on the high energy side of the absorption edge of an element has been shown to be due to modifications to the final state wave function of the ejected photoelectron from the absorbing atom by its near neighbors.('1,2,3) Consequently, the EXAFS provides a probe of the local environment of the absorbing atom and can be analyzed to yield structural information such as bond distances or coordination numbers.('4) Thus, the EXAFS provides a structural tool potentially applicable to crystalline, polycrystalline, amorphous, liquid, or gas phase materials.The applicability of EXAFS techniques to the problems of determining structures of intrazeolitic compounds is demonstrated. It is found that the EXAFS, with its insensitivity to long range structure, can give accurate descriptions of local environments of exchanged transition metal ions in large (Y) and small (A) pore zeolites. The results show that in the large pore cobalt-Y zeolite hydrate,('5) the large pore manganese-Y zeolite hydrate, and the small pore manganese-A zeolite hydrate, the coordination of the cations are identical to that in aqueous solutions. In the small pore cobalt-A zeolite hydrate, though, the cobalt cation is pentacoordinate.('5) However, in no hydrated zeolites is there any evidence of second shell backscattering that would indicate coordination to the zeolite framework.The EXAFS results on the dehydrated cobalt('6) and manganese exchanged A zeolites show second shell interactions, qualitatively consistent with single crystal X-ray diffraction studies, that indicate that the exchanged cations in the dehydrated zeolites are localized in the zeolite framework in or near the center of the "six-rings" of the zeolite supercage.('1)E. A. Stern, Phys. Rev. B10, 3027 (1974). ('2)P. A. Lee and B. J. Pendry, Phys. Rev. B11, 2795 (1975). ('3)C. A. Ashley and S. Doniach, Phys. Rev. B11, 1279 (1975). ('4)E. A. Stern, D. E. Sayers, and F. W. Lytle, Phys. Rev. B11, 4836 (1974). ('5)T. I. Morrison, A. H. Reis, Jr., E. Gebert, L. E. Iton, G. D. Stucky, and S. L. Suib, J. Chem. Phys. 72, 6276 (1980). ('6)T. I. Morrison, L. E. Iton, G. K. Shenoy, G. D. Stucky, S. L. Suib, and A. H. Reis, Jr., J. Chem. Phys. (in press).U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD