Regresar

Combined Experimental and Theoretical Study of Methyl Acetoacetate Adsorption on Ni{100}

Abstract:

The enantioselective hydrogenation of methyl acetoacetate (MAA) over modified Ni-based catalysts is a key reaction in the understanding of enantioselective heterogeneous catalysis as it represents the only example of this class of reactions catalyzed by base metals. Yet, there is very little molecular-level information available about the adsorption complex formed by the reactants on Ni surfaces. Here, we report a combined experimental and theoretical study of the adsorption of MAA on the Ni{100} surface. X-ray photoelectron spectroscopy shows that MAA forms stable multilayers at low temperatures, which desorb between 200 and 220 K. At higher temperatures a single chemisorbed layer is formed, which decomposes between 300 and 350 K. Density functional theory modeling pbkp_redicts an enolate species with bidentate coordination as the most stable chemisorbed species. Comparison of photoelectron spectroscopy and X-ray absorption data with simulations using this adsorption model show good qualitative and quantitative agreement. The molecular plane is tilted with respect to the surface plane by about 50°. This breaking of symmetry provides a mechanism for the enantioselective hydrogenation.