Density functional theory study on catalytic cracking of n-hexane on heteropoly acid: A comparison with acidic zeolite.

We have performed a direct comparison of n-hexane cracking catalysed by a zeolite (H-ZSM-5) and a heteropoly acid (phosphotungstic acid, HPW). This comparison was examined by employing density functional theory, including dispersion energy, M06-L, for the purpose of understanding these two catalysts for this industrially important reaction. The predicted adsorption energies of hexane are −21.4 and −6.8 kcal/mol for H-ZSM-5 and HPW, respectively. The protolytic cracking mechanism is proposed to proceed via the first step of the C-C activation and is found to be the rate-determining step with activation energies of 42.8 and 41.4 kcal/mol for H-ZSM-5 and HPW, respectively. We also discuss the advantages and disadvantages of both catalysts for hydrocarbon cracking and give a perspective of utilising cutting-edge molecular design for a tailor-made hybrid catalyst. © 2011 Canadian Society for Chemical Engineering [ABSTRACT FROM AUTHOR]