, Volume 24, Issue 4, pp 1307-1318

Structures and mechanisms of the dehydration of benzaldoxime over Fe-ZSM-5 zeolites: a DFT study

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Abstract

With considerable academic and industrial attention being focused on green chemical processes, environmentally friendly nanomaterials such as zeolites have been systemically modified and tuned to meet such requirements in various industrial chemical reactions. The dehydration of benzaldoxime over Fe-ZSM-5 zeolite has thus been systematically investigated by means of the ONIOM(M06:UFF) scheme. Three different forms of iron-oxo species are used for the active center of Fe-ZSM-5: (a) [FeO]+, (b) [FeO2]+, and (c) [Fe(OH)2]+. Both the oxidative and polar elimination mechanisms for the dehydration process were investigated. For the oxidative dehydration mechanism, this route begins with the oxygen-end benzaldoxime adsorption complex. The energy barrier is calculated to be 24.5, 31.4, and 33.6 kcal/mol for [FeO]+Z, [FeO2]+Z, and [Fe(OH)2]+Z, respectively. These are significantly lower than the energy barrier found for the polar elimination one. A comparison of the energetic profiles suggest that the dehydration process would take place through the oxidative dehydration mechanism in which the [FeO]+Z is the most reactive form of mononuclear Fe-ZSM-5 zeolite. Over the [FeO]+Z, an α-oxygen has the function of migrating the hydrogen of the benzaldoxime and the hydroxyl group of substrate that consecutively leads to bonding with the metal center to produce the [Fe(OH)2]+Z and the benzonitrile product.