The mechanism of ethanol dehydrogenation to acetaldehyde over Au/ZSM-5 zeolite was investigated by using the density functional M06-L method. A 12T quantum cluster has been employed to model the Au/ZSM-5 zeolite, where T refers Si or Al atoms. The reaction commences with ethanol being adsorbed on the Au active site of the zeolitic framework. The adsorption energy is predicted to be �39.7 kcal/mol. In the next step, the ethoxide intermediate is produced via the dehydrogenation of the OH group of the adsorbed ethanol with the activation energy of 43.2 kcal/mol. This step is found to be the rate-determining step which is the same trend of the ethanol dehydrogenation on Au surfaces. Consequently, the ethoxide intermediate is decomposed into acetaldehyde and hydrogen products by way of the transfer of the hydrogen at the methylene carbon to interact with the hydrogen at the Au site. This step is more facile than the first step, and needs a much lower activation barrier of 30.8 kcal/mol. We also found that the supported zeolite facilitates the ethanol OH dehydrogenation on the Au site and plays a role in stabilizing the species in the reaction coordinates as well as the transition state and intermediate complexs over the bare Au system.

Dehydrogenation of ethanol to acetaldehyde over Au-exchanged ZSM-5 zeolite: A DFT study

247th National Meeting (2014)

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