First-principle investigation on catalytic hydrogenation of benzaldehyde over Pt-group metals

Understanding the hydrogenation of organic compounds in the aqueous phase has always been fundamentally important for improving carbon neutral pathways to fuels and value-added chemicals. In this study, we investigated both thermodynamic and kinetic profiles of benzaldehyde hydrogenation over the Pd(111) and Pt(111) metal surfaces using density functional theory (DFT) and ab initio molecular dynamic (AIMD) simulations. The adsorption of H₂ shows the mixed preference of H adsorption sites on the Pt(111), while the fcc adsorption site is dominant for H on the Pd(111). When benzaldehyde is added to the systems, we observe a strong reduction of benzaldehyde on charged Pd (111) surface compared with that on neutral surface. In contrast, charged state of the Pt(111) surface does not change their interaction. Subsequent hydrogenation reaction of benzaldehyde over Pd(111), proceeding via Langmuir-Hinshelwood mechanism, is affected by two major factors: the presence of H₂O solvent and surface charge. The presence of H₂O solvent greatly reduces the activation energy of C–H and O–H bond formation during the hydrogenation process. Furthermore, the hydrogenation step via C–H bond formation is preferred thermodynamically and kinetically over O–H bond formation during thermocatalytic hydrogenation, while the opposite trend holds true during electrocatalytic hydrogenation.