Abstract
The ratio of cracking to hydrogen transfer for n-heptane and gasoil increases with increasing dealumination of HYUS samples. In gasoil cracking, a sharp increase in this ratio occurs for samples with less than 10 Al per unit cell (uc). The adsorption of n-butane and 1-butene on HYUS samples shows that the amount of these gases adsorbed decreases with increasing dealumination. A decrease in the effective concentration of the product on the zeolites would favour monomolecular (cracking) over bimolecular (hydrogen transfer) reactions. The ratio of 1-butene to n-butane adsorbed decreases considerably below 10 Al/uc, indicating a less selective adsorption of olefins with respect to paraffins when the hydrophobicity (framework silicon-to-aluminium ratio) of the zeolites increases. These adsorption effects have an important influence on the cracking-to-hydrogen transfer ratio observed, as the hydrogen transfer reactions necessarily involve olefins, whereas cracking of n-heptane at low conversions and of paraffinic gasoil involves mainly paraffins.
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