The adsorption of saturated and unsaturated hydrocarbons on nanostructured zeolites (H-MOR and H-FAU): An ONIOM study

Abstract

The adsorption and interactions of light alkanes and alkenes on acidic zeolites (H-MOR and H-FAU) were theoretically studied using the ONIOM approach. With the basis set superposition error (BSSE) corrections, the ONIOM(MP2/6-31G(d,p):UFF//B3LYP/6-31G(d,p):UFF) adsorption energies of alkanes (ethane, propane, and n-butane) in H-FAU and H-MOR were in good agreement with the experimental measurements. For adsorption of alkenes in acidic zeolite which is not possible to experimentally measure, the adsorption energies were predicted to be -9.4, -11.3, and -12.5 kcal/mol for ethene, propene, and 1-butene in H-FAU, respectively and -10.1, -13.8, and -17.4 kcal/mol for ethene, propene, and 1-butene in H-MOR, respectively. It was found that the extended zeolitic framework covering the nanocavity was essential for describing the confinement effect of the zeolites and led to the differentiation of different types of zeolites. These results suggest that this ONIOM scheme is a practical method for investigating the adsorption of unsaturated and saturated hydrocarbons on these zeolites. © 2007 Elsevier B.V. All rights reserved.