Acidic and catalytic properties of the Ca-Pt-H-mordenite system

Abstract

The acid strength distribution and catalytic behavior (activity, selectivity, and deactivation in the reactions of ortho-xylene) of H-mordenite (HM), calcium mordenite (CaM), platinum H-mordenite (PtHM), calcium platinum H-mordenite (CaPtHM) and calcium platinum H-dealuminated-mor-denite (DCaPtHM) have been studied. Measurement of the isosteric heats of adsorption of NH₃ indicate that the concentration of strong acid sites in these catalysts follow the order: HM > DCaPtHM > CaPtHM > PtHM > CaM. Their initial activity for the conversion of ortho-xylene decreases as HM > DCaPtHM > PtHM > CaPtHM > CaM. The selectivity of these catalysts in yielding isomeric xylenes rather than non-C₈ aromatics by disproportionation reaction decreases in the following order: CaM > DCaPtHM > HM > CaPtHM > PtHM. The catalyst undergo deactivation due to coke formation in the following order: HM > DCaPtHM > CaPtHM > PtHM=CaM. An attempt is made to correlate the observed catalytic behavior with the acidic and steric features of the catalysts.