Unraveling the ligand effect on acrolein hydrogenation on Pd(111): Insights from first-principles calculations

Selective conversion of multifunctional organic molecules is a central challenge in sustainable chemical production. Acrolein serves as an ideal model to explore such transformations. Specifically, functionalization of the Pd(111) surface with ligand molecules has been experimentally shown to improve the selectivity of acrolein hydrogenation into propenol. Previous DFT studies have suggested that the selectivity of acrolein hydrogenation is highly sensitive to the surface coverage, with high coverage reducing selectivity and low coverage increasing it. Here, we have used DFT to investigate the formation of the ligand layer and the thermodynamics and kinetics of acrolein hydrogenation on the Pd(111) modified with oxopropyl and N-butylimine ligands. These calculations were complemented with IR spectroscopy measurements, which provide direct evidence of ligand binding modes and reaction intermediates, offering experimental benchmarks to calibrate the theoretical predictions. Our calculations demonstrate that in the presence of ligands, acrolein adopts a flat adsorption geometry, typical to low surface coverage, which facilitates kinetically favorable hydrogenation of the C=O bond and steers selectivity towards alcohols. Overall, our work demonstrates that surface ligand functionalization does not alter the reaction mechanism, as previously suggested, but instead creates reaction pockets with a favorable reactant adsorption geometry to achieve the desired selectivity. • An extensive study of the selective acrolein hydrogenation on ligand functionalized Pd(111). • Ligand functionalization creates “reaction pockets” where acrolein can adopt a flat adsorption geometry, mimicking low-coverage conditions that favor C=O hydrogenation. • Steric repulsion between ligands and adsorbates weakens the adsorption on oxopropyl functionalized Pd(111).