On the Limited Role of Electronic Support Effects in Selective Alkyne Hydrogenation: A Kinetic Study of Au/MOx Catalysts Prepared from Oleylamine-Capped Colloidal Nanoparticles

We report a quantitative kinetic evaluation and study of support effects for partial alkyne hydrogenation using oleylamine-capped Au colloids as catalyst precursors. The amine capping agents can be removed under reducing conditions, generating supported Au nanoparticles of similar to 2.5 nm in diameter. The catalysts showed high alkene selectivity (>90%) at all con- versions during alkyne partial hydrogenation. Catalytic activity, observed rate constants, and apparent activation energies (25-40 kJ/mol) were similar for all Au catalysts, indicating support effects are relatively small. Alkyne adsorption, probed with FTIR and DFT, showed adsorption on the support was associated with hydrogen-bonding interactions. DFT calculations indicate strong alkyne adsorption on Au sites, with the strongest adsorption sites at the metal-support interface (MSI). The catalysts had similar hydrogen reaction orders (0.7-0.9), and 1-octyne reaction orders (similar to-0.2), suggesting a common mechanism. The reaction kinetics are most consistent with a mechanism involving the non-competitive activated adsorption of H-2 on an alkyne-covered Au surface.