Adsorption constants and heats of adsorption of different types of hydrocarbons on zeolitic catalysts have been obtained under cracking reaction conditions, by means of kinetic techniques. The heat of adsorption of a naphthene is very close to the alkane with the same number of carbon–carbon bonds, which in turn is defined by the van der Waals interactions between the hydrocarbon and the zeolite walls. The presence of the double bond in the olefin increases the heat of adsorption of the corresponding alkane by ∼40 kJ/mol. Comparison of decalin and tetralin shows the contribution of the aromatic ring to the heat of adsorption. Differences in heat of adsorption not only explain differences in cracking conversion, but can also predict variations in catalyst decay when industrial feeds of different compositions are used.
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