Density Functional Theory Study of the Dehydrogenation of Ethanoi to Acetaldehyde over the Au-Exchanged ZSM-5 Zeolite: Effect of Surface Oxygen

摘要

The transformation of ethanol, one of the low-cost biomass products, into fine chemicals has received considerable attention related to the development of clean industrial technologies. We calculated the reaction mechanism of ethanoi dehydrogenation to acetaldehyde over Au-exchanged ZSM-S zeolite with and without surface oxygen by means of the density functional theory. The reaction is proposed to proceed in two steps. In the first, dissociation of the ethanoi O-H bond leads to an ethoxide intermediate which is then converted to acetaldehyde. The reaction barrier for the first step is 9.0 kcal/mol for the Au-O/ZSM-5 zeolite, much smaller than for the Au/ZSM-5 zeolite (43.0 kcal/mol). For step 2, the reaction barriers are 4.4 kcal/mol for Au-O/ZSM-5 and 30.8 kcal/mol for Au/ZSM-5, respectively. The results indicate that the presence of surface oxygen on the Au site assists both the ethanoi O-H bond dissociation and the conversion of ethoxide to acetaldehyde.