REDUCIBILITY OF RHENIUM IN PT-RE/AL2O3 REFORMING CATALYSTS - A TEMPERATURE PROGRAMMED REDUCTION X-RAY ABSORPTION NEAR-EDGE STRUCTURE STUDY

摘要

Temperature programmed reduction (TPR) experiments were performed on Pt-Re/Al2O3 catalysts in an X-ray absorption near-edge structure (XANES) apparatus to assess the effect of different metal loadings and different Re/Pt ratios on the reducibility of Re. It was found that these two variables affect the reduction kinetics of Re, but they do not seem to affect the final oxidation state of the Re metal. The performance of these catalysts under reforming conditions appears to correlate with the mode of metal particle generation of the samples, as monitored by the TPR-XANES technique. Catalyst performance data have been generated in a laboratory bench scale unit as well as in a pilot plant unit. The relative binding energy (BE) of core p electrons of Re in the catalysts with respect to an appropriate internal reference was monitored at both the L(II) and L(III) edges as a function of the reduction temperature. Such a comparison served as a test to confirm that the kinetics of Re reduction as monitored by the TPR-XANES technique is independent of the edge chosen. We were unable to obtain a precise two-shell fitting of the Pt-Re by EXAFS. This type of fitting is complicated by backscattering by oxygen in the alumina lattice after reduction, providing too large a number of independent parameters for a reliable fitting. (C) 1995 Academic Press, Inc. [References: 13]