n-Hexane cracking at high pressures on H-ZSM-5, H-BEA, H-MOR, and USY for endothermic reforming

• High-pressure n-hexane cracking was studied over H-ZSM-5, H-BEA, H-MOR, and USY.
• Cracking behavior showed characteristics of bimolecular mechanism at high pressures.
• Pore size affects which process is dominant for high-pressure cracking.
• H-ZSM-5 is preferred for endothermic fuel reforming.

Catalytic cracking of n-hexane was studied over H-ZSM-5, H-BEA, H-MOR, and USY zeolites at pressures between 1 and 137 bar and temperatures between 573 and 673 K, for application to endothermic reforming for cooling of aircraft engines. While the product distributions over each zeolite exhibited characteristics of a bimolecular mechanism, the product distributions were distinctly different on H-ZSM-5, exhibiting much less isomerization and more C-4 and C-5 products. Furthermore, in contrast to results on the larger pore zeolites, the reaction rates on H-ZSM-5 followed a simple Langmuir–Hinshelwood rate expression over the entire range of pressures and were stable for at least several hours at all pressures. Reaction rates on H-BEA, H-MOR, and USY were only weakly dependent on pressure and also exhibited an induction period at 137 bar before decreasing with time. Implications of these results for endothermic reforming are discussed.

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