FORMATION OF PDFE ALLOY CLUSTERS IN ZEOLITE-Y

Reduction of ion-exchanged PdFe/NaY with H-2 at 773 K results in the f ormation of Fe2+ ions and PdFe alloy clusters; no FeO is formed by red ucing Fe/NaY. The extent of Pd-enhanced reduction of Fe2+ to FeO decre ases with increasing proton concentration in the zeolite. Data obtaine d by Mossbauer spectroscopy, ferromagnetic resonance, and FTIR of adso rbed CO indicate prevalent formation of PdFe alloy clusters. Temperatu re-programmed reduction (TPR) and desorption (TPD) show the extent of Fe reduction and the reoxidation by zeolite protons of FeO in bimetal particles. An average composition of Pd16Fe and Pd10Fe3 was found for the reduced clusters in PdFe/NaHY and neutralized PdFe/NaY, respective ly. No alpha-Pd hydride is formed with PdFe(x) under conditions where this hydride is prevalent for unalloyed Pd clusters. The propensity to form Pd hydride is restored by oxidative leaching of the Fe atoms fro m the bimetallic clusters. A strong ferromagnetic resonance signal fro m PdFe(x) particles isolated in different zeolite cages and containing only one or two Fe atoms suggests that Pd atoms surrounding an Fe ato m become polarized.