Surface Chemistry of Alanine on Ni{111}

The adsorption of l-alanine on Ni{111} has been studied as a model of enantioselective heterogeneous catalysts. Synchrotron-based X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to determine the chemical state, bond coordination, and out-of-plane orientation of the molecule on the surface. Alanine adsorbs in anionic and zwitterionic forms between 250 and approximate to 320 K. NEXAFS spectra exhibit a strong angular dependence of the pi* resonance associated with the carboxylate group, which is compatible with two distinct orientations with respect to the surface corresponding to the bidentate and tridentate binding modes. Desorption and decomposition begin together at approximate to 300 K, with decomposition occurring in a multistep process up to approximate to 450 K. Comparison with previous studies of amino acid adsorption on metal surfaces shows that this is among the lowest decomposition temperatures found so far and lower than typical temperatures used for hydrogenation reactions where modified Ni catalysts are used.