Radiotracer experiments on carbon formation in zeolites

The origin of carbon deposits in zeolite catalysts was traced with radioactively labeled mixtures of hexane and aromatics (100 to 500 psia H2). Over mordenite and Y catalysts of varying aluminum content it was shown that the participation of aromatics in coke formation was equal to or exceeded that of the paraffin. Such participation decreased with increasing temperature or, in the case of mordenite, with increasing SiO2/Al2O3 ratio, but was little affected by changes in hydrogen pressure. It was concluded that the alkylation of aromatics is the initial step in coke formation in the present experiments and that hydrogen transfer, an important reaction in the subsequent transformations of carbon deposit, need not be invoked to explain the original deposition