J. Phys. Colloques
Volume 47, Numéro C8, Décembre 1986EXAFS and Near Edge Structure IV
|Page(s)||C8-231 - C8-236|
J. Phys. Colloques 47 (1986) C8-231-C8-236
EXAFS STUDIES ON THE REDUCTION OF Pd(II) IN X ZEOLITESK. MÖLLER1, 2 et T. BEIN3, 4
1 Center for Catalytic Science and Technology, Department of Chemical Engineering, University of Delaware, Newark, DE 19716, U.S.A.
2 Department of Chemical Engineering, University of New Mexico, Albuquerque, NM 87131, U.S.A.
3 E.I. Dupont de Nemours and Company, Central Research and Development Department, Experimental Station, Wilmington, DE 19898, U.S.A.
4 Department of Chemistry, University of New Mexico, Albuquerque, NM 87131, U.S.A.
Palladium tetraammine ion exchange into zeolite, temperature treatments under different atmospheres, and hydrogen reduction have been studied by EXAFS at the Pd K edge. Complete autoreduction is found to take place between 473 and 623 K under vacuum. A bidisperse Pd metal phase is formed which agglomerates at the expense of the small particles upon prolonged heating at 623 K. In contrast, a similar treatment under oxygen suppresses autoreduction, and the Pd cations remain in zeolite coordination sites. Additional small amounts of palladium oxide are observed under these conditions. If hydrogen is admitted to the dehydrated, ionic system at 295 K, the oxygen coordination of the Pd disappears and evidence is obtained for the formation of Pd(0) dimers that interact with the framework via a long Pd-0 bond.