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

Abstract

AbstractWe 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