CHARACTERIZATION OF ZEOLITE-SUPPORTED PT-CU BIMETALLIC CATALYST BY XE-129 NMR AND EXAFS

Abstract

Samples of platinum supported on NaY zeolite (Pt/NaY), Cu/NaY, and bimetallic PtCu/NaY have been prepared by using a scheme that consists of ion exchange of the metalammine cations, activation in flowing O2, and subsequent reduction in H2. These samples have been characterized by 129Xe NMR and extended X-ray absorption fine structure (EXAFS). The chemical shift in 129Xe NMR of the xenon adsorbed on PtCu/NaY has been found to be significantly lower than that on Pt/NaY with the same Pt content under the same experimental conditions, and therefore bimetallic PtCu clusters are formed in supercages of NaY zeolite in both the cases of a sequential clustering method and a simultaneous ion exchange preparation method. The peak intensities at Pt-Pt coordination distance in the Fourier transforms of EXAFS spectra for Pt/NaY and PtCu/NaY are very similar, which indicates that the reduction of Cu precursor has resulted in no appreciable changes in the PtPt coordination structure of the Pt cluster. It thus appears, from these results, that during the reduction of Cu precursor the bimetallic PtCu clusters are formed with a model of a Cu covering on Pt clusters in the supercage of NaY zeolite. © 1992.