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Octadecane was isomerized over three different Pt/H-ZSM-23 samples. The distributions of methylheptadecane and dimethylheptadecane skeletal isomers obtained on the Pt/ZSM-23 samples were very similar. Positional isomer distributions are fingerprints of the zeolite framework structure. The independence of skeletal isomer distributions from Al-gradients and particle size constitutes a strong argument in favor of pore-mouth catalysis.

A unified model for the description of vapor- and liquid-phase hydroconversion has been developed. The high isomer yield, which is typical for the shape selectivity exhibited by Pt/H−ZSM-22 at vapor-phase conditions, is still observed at liquid-phase conditions. However, the molar cracking yield is enhanced by at least 10 mol % when operating at liquid-phase conditions. The latter effect is mainly due to an increased physisorption competitiveness of lighter alkanes, which also results in enhanced cracking of lighter alkanes. The effect amounts to approximately 3 orders of magnitude for a difference of 2 in carbon number. These aggregation state effects are accounted for in the model through (i) liquid phase thermodynamic nonideality, (ii) destabilization of the physisorbed state by compression of the adsorbate by the bulk fluid, and (iii) carbenium ion stabilization by sorbent solvation by the bulk fluid. F-values of the order of 103 indicate the model's adequacy in describing the observed phenomena.