The surface alkoxy species formation is an important step for chemical reaction in the zeolite framework. This is the starting step and it is found to be a rate determining step for important chemical reactions. In this study, the adsorption and surface alkoxy species formation of ethylene on acidic zeolites between conventional zeolite (H-ZSM-5) and a new zeolite (H-ITQ-22) have been carried out using the well calibrated ONIOM (MP2/6-31G(d,p):M06-2X/6-31G(d,p))  approach. The adsorption energies of ethylene are predicted to be -13.2 and -13.7 kcal/mol for H-ZSM-5 (5T:34T) and H-ITQ-22 (5T:42T), respectively. However, their activation energies are noticeably different from their adsorption energies and being 27.8 and 23.8 kcal/mol for H-ZSM-5 and H-ITQ-22, respectively are due mainly to their confinement effect. The ethoxy product strongly interacts with H-ITQ-22 (-27.6 kcal/mol) than H-ZSM-5 (-19.7 kcal/mol). Our findings are important for studying reaction mechanisms in zeolite catalysts.

Density functional study of adsorption and surface alkoxy species formation of ethylene on a newly synthesized H-ITQ-22 zeolite: A comparison with a well-known and industrially important H-ZSM-5 zeolite

243rd National Meeting (2012)

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