SYNERGISM OF PT/GAMMA-AL2O3 AND PT/BETA ZEOLITE IN THE REFORMING OF NAPHTHENES

Composite catalysts of Pt supported on both zeolite beta and gamma-Al2O3 are employed for the reforming of methylcyclopentane and methylcyclohexane. Due to its relatively high Pt dispersion, Pt/gamma-Al2O3 is responsible for dehydrogenation reactions leading to methylcycloolefins. Pt/beta zeolite, which has a much higher Bronsted acidity thany-Al2O3, is responsible for the bimolecular alkylation reactions leading to aromatics, the transalkylation reactions of aromatics, and the isomerization reactions of methylcycloolefins to C6 cycloolefins which further via dehydrogenation lead to benzene. The residence time plays an important role because the dehydroisomerization reactions are much slower than the bimolecular alkylation reactions. At a high residence time and with methylcyclopentane as feed, the composites generate a synergistic effect which leads to a maximum in the benzene yield at about 40 wt % Pt/beta zeolite. With methylcyclohexane as feed, high aromatic (mainly toluene) yields are obtained for zeolite contents below 30 wt %. Bimolecular alkylation reactions, which are stimulated by the zeolite pore structure and the high Bronsted acidity of zeolite beta, also occur and lead to aromatics with a larger number of carbon atoms than the feed naphthene and to a better utilization Of C<6 olefins and paraffins generated by cracking. Beneficial effects can be achieved by balancing the acidic with the dehydrogenation functions of a reforming catalyst through the incorporation of Pt/beta zeolite into Pt/gamma-Al2O3.