Abstract
The role of water in the aldol condensation process is known to be very important but not fully understood. In this study, density functional theory (DFT) and microkinetic modeling (MKM) are employed to qualitatively and quantitatively investigate the role of water in the aldol condensation reaction on Zr-BEA, leading to the formation of crotonaldehyde, sorbaldehyde, and octatrienal. The study encompasses each step of the condensation process, including adsorption, dehydrogenation, C-C coupling, and dehydration. The DFT simulation results indicate that water influences on the aldol condensation process through changing the reaction pathway and redistributing electron density. Co-adsorbed water molecules can facilitate the dehydration of the coupling product CH2RCHOCH2CHO* through intermolecular hydrogen transfer, significantly reducing the energy barrier. Additionally, the presence of water changes the electron density, enhancing dehydrogenation while suppressing C-C coupling and adsorption process slightly. To quantitatively assess the extent of water's impact, MKM is applied to simulate all elementary reactions, adsorption, and desorption processes. The results indicate that the H2O* generated by dehydrogenation tends to desorb, and the subsequent condensation process undergoes intramolecular hydrogen transfer. When water is present in the reactants, the condensation process shifts from intramolecular to intermolecular hydrogen transfer. Notably, water exerts a significant inhibitory effect on the formation of octatrienal, while it does not compromise the formation of crotonaldehyde and sorbaldehyde. The role of water clarified in this paper should be kept in mind in future studies to explore the strategic of enhancing the production of aldehyde products.
Published Version
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