(6b) The Effect of Dynamic Nature of Water on the Hydrogenation Pathway

Understanding of the effect of solvents on heterogenous catalysis is valuable for potential applications in chemical industry. Although extensive experimental and theoretical studies have been carried out, only few studies have focused on how dynamic nature of solvents affects the underlying mechanism that solvent involved directly in the reaction pathway. In this work, we used AIMD simulations and DFT calculations with an explicit solvent to study the selective C=O hydrogenation of furfural as the probe. Specially, we investigated how water can modulate the hydrogenation pathway in an aqueous phase and the role of entropy at the solid/liquid interface on the overall kinetics of this reaction. We found that water does not intervene the direct hydrogenation reaction pathway; alternatively, the dynamics of water, which is related to the hydrogen-bonding network of the solvent at the solvent/solid interface, only stabilizes the intermediates, leading to a lower energy barrier. Interestingly, we revealed that the relative position of water molecules and the surface hydrogen atoms can influence the activation energy in the proton shuttling pathways. In particular, water molecules in the proximity to hydrogen atoms can pick up the hydrogen atoms located at bridge or hollow sites to facilitate this reaction with lower barrier than the direct pathway. In contrast, a collective motion is required for water to pick up hydrogen atoms and form the hydrogen-bonding with C=O, initiating the hydrogenation reaction. In this case, the reaction barrier strongly depends on the hydrogen-bonding network of the water solvent so that the barrier of this pathway could be lower or higher than the direct pathway. In addition, we calculated the reaction free energy barrier by applying metadynamics simulations. This work provides fundamental understanding of the hydrogenation kinetics under a liquid phase on metal catalysts, i.e., how dynamics of water can influent the reaction pathway.