COKING, AGING AND REGENERATION OF ZEOLITES .11. COKE FORMATION AND DEACTIVATION OF PT-ULTRA STABLE ZEOLITE HY AND PTH-MORDENITE CATALYSTS DURING HYDROGENATION OF BENZENE

A significant amount of carbonaceous compounds (coke) is formed during benzene hydrogenation at 80°C on Pt-Ultrastable Zeolite HY (PtUSHY) and PtH-mordenite (PtHMOR) catalysts. These compounds, deposited in the large channels of PtHMOR, block the access of benzene to the platinum crystallites situated in these channels, causing almost immediate deactivation of this catalyst. With PtUSHY the deactivating effect of coke is much less. Benzene hydrogenation, often used for characterizing the hydrogenating sites of metal catalysts, cannot be used when the metal is deposited in a one-dimensional acid zeolite such as HMOR. With both Pt zeolites the coke components consist of several C6-naphthene units (cyclohexane or methylcyclopentane) associated in certain instances with benzenic units. The number of units depends on the catalyst: three with PtHMOR, three to five with PtUSHY. All these compounds result from reactions between benzene and cyclohexane molecules followed by isomerization of the cyclohexane units. The acid and the metallic sites participate in these reactions (bifunctional catalysis). © 1990.