A density functional study on the effect of the zeolite cavity on its catalytic activity: The dehydrogenation and cracking reactions of isobutane over HZSM-5 and HY zeolites

The dehydrogenation and cracking reactions of isobutane over HZMS-5 and HY were studied at the DFT level of calculation to verify the influence of the cavity on the energetics and mechanism of the reactions. The zeolites were represented by the 20T and 32T clusters, respectively. The results indicate that the reactions follow the same mechanism in both zeolites but the activation energies are reduced by ∼10 kcal/mol relative to the values with smaller clusters. Activation energies for the dehydrogenation reactions were similar in both zeolites, but for the cracking reaction in HY, the activation energy is ∼5 kcal/mol higher than in HZSM-5.