Quantifying Enhancement of Metal-Supported Zeolites Due to Hydrogen Spillover

As bifunctional catalysts, metal-supported zeolites play an important role in refining and petrochemical processes, e.g. isomerisation, alkylation, etc. Reduction in acidity and acid strength of zeolites upon their impregnation with metals have been widely reported. Also hydrogen spillover vis-a-vis the closeness of two catalyst functions (acid and metal) has been discussed at length. Hydrogen spillover has been claimed to give rise to formation of additional acid sites on supports. Here quantification of acid sites for two zeolites, zeolite Y and ZSM-5, impregnated with different metals in various proportions after exposing them to hydrogen, has been attempted using ammonia temperature programmed desorption. The observed acidity values have been explained on the basis of metal cluster size.