A Computational Study of Direct CO2 Hydrogenation to Methanol on Pd Catalysts

We investigate the mechanism of direct CO₂ hydrogenation to methanol on Pd (111), (100) and (110) surfaces using density functional theory (DFT), providing insight into the reactivity of CO₂ on Pd-based catalysts. The initial chemisorption of CO₂, forming a partially charged CO₂^δ-, is weakly endothermic on a Pd (111) surface, with an adsorption energy of 0.06 eV, and slightly exothermic on Pd (100) and (110) surfaces, with adsorption energies of -0.13 and -0.23 eV, respectively. Based on Mulliken analysis, we attribute the low stability of CO₂^δ- on the Pd (111) surface to a negative charge that accumulates on the surface Pd atoms interacting directly with the CO₂^δ- adsorbate. For the reaction of the adsorbed species on the Pd surface, HCOOH hydrogenation to H₂COOH is predicted to be the rate determining step of the conversion to methanol in all cases, with activation barriers of 1.35, 1.26, and 0.92 eV on Pd (111), (100) and (110) surfaces, respectively.