CO HYDROGENATION OVER PDNIX ALLOYS ENCAGED IN NAY ZEOLITE

Bimetallic (Pd + Ni)/NaY samples were studied and compared with monometallic Pd/NaY and Ni/NaY samples and their physical mixture. Samples were characterized by XRD, XPS, and CO hydrogenation. The formation of PdNix alloy particles encaged in NaY zeolite was found for the bimetallic samples. Under conditions of CO hydrogenation, significant changes in sizes and distributions of Pd, Ni, and PdNix particles take place. Metal particle growth is accompanied by local collapse of the zeolite lattice. The selectivity of PdNix alloys for methane formation was significantly higher than that of monometallic Pd or Ni particles or of their physical mixtures. On mixed PdNix ensembles the rate of CO dissociation and/or CHx hydrogenation appears to be enhanced with respect to monometallic ensembles. Acid "leaching" of Ni by zeolite protons from alloy particles restores a metal surface rich in Pd, leading to an enhanced selectivity to methanol and its consecutive products, dimethyl ether and higher hydrocarbons. © 1992.