The mechanism of ethanol dehydrogenation to acetaldehyde over Fe-ZSM-5 zeolite was investigated by using the density functional M06-L method. A 12T quantum cluster has been employed to model the Fe-ZSM-5 zeolite, where T refers Si or Al atoms. The reaction commences with ethanol being adsorbed on the FeO2+ active site of the zeolitic framework. The adsorption energy is predicted to be -29.2 kcal/mol and compares well with the MP2 level of theory with the positive advantage that it needed only a fraction of the CPU time. The next step, the ethoxide-hydroxide intermediate is produced via the hydrogen abstraction from the adsorbed ethanol OH group to active oxygen of FeO2+. This step is found to be the rate-determining step with the activation energy of 22.2 kcal/mol. Consequently, the ethoxide-hydroxide intermediate is decomposed into acetaldehyde by way of the hydrogen abstraction from the methylene carbon of ethoxide to hydroxyl group. This step is more facile than the first step, and needs a much lower activation barrier of 8.3 kcal/mol. The results indicate that Fe -ZSM-5 zeolite is a highly active catalyst for the dehydrogenation of ethanol to acetaldehyde.

Adsorption and dehydrogenation of ethanol over Fe-ZSM-5 zeolite: A DFT mechanistic study

243rd National Meeting (2012)

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