CO-Oxidation on Size-Selected Pt Clusters and Enantioselective Adsorption on PdGa Surfaces

Catalysis studies on size-selected metal clusters deposited onto single-crystal surfaces often tacitly assume that the clusters where the reaction takes place are having the size of the initially deposited ones, and that the substrate itself does not contribute much to the reaction. We show with the CO oxidation on size-selected Pt clusters on rutile TiO2(110) a counterexample. The oxidation state of the substrate plays an important role [1] and the clusters show significant ripening at the temperature where the reaction takes place, and this ripening is enhanced by the reaction enthalpy [2].<\p>PdGa surfaces are anticipated to be more selective in hydrogenation reactions, e.g., of acetylene to ethylene. Due to the crystal structure of PdGa, the (111) and the (-1-1-1) surfaces are not equivalent. One exhibits Pd trimers the other Pd monomers. In both cases, these reaction sites are well separated by the less reactive Ga atoms [3]. We present experiments revealing the adsorption sites of small hydrocarbons [4] and of CO [5], demonstrating the ensemble effect. We further show that the chirality of the two surfaces leads to enantioselective adsorption of the prochiral molecule 9-Ethynylphenanthrene [6].<\p>We finally show the spectroscopy of molecular rotations with the STM for the case of H2 and its isotopes physisorbed on graphene and hexagonal boron-nitride layers grown on metal surfaces. Since the rotational excitation energies are different for ortho and para H2, we are able to discern the nuclear spin isomers [7,8].<\p>[1] S. Bonanni, K. Aït-Mansour, W. Harbich and H. Brune, J. Am. Chem. Soc. 134, 3445 (2012). <\p> [2] S. Bonanni, K. Aït-Mansour, W. Harbich and H. Brune, J. Am. Chem. Soc. 136, 8702 (2014). <\p> [3] J. Prinz et al., Angew. Chem. Int. Ed. 51, 9339 (2012). <\p> [4] J. Prinz et al., J. Am. Chem. Soc. 136, 11792 (2014). <\p> [5] J. Prinz et al., J. Phys. Chem. C 118, 12260 (2014). <\p> [6] J. Prinz, H. Brune, O. Gröning and R. Widmer, Angew. Chem. Int. Ed., submitted (2014). <\p> [7] F. D. Natterer, F. Patthey and H. Brune, Phys. Rev. Lett. 111, 175303 (2013). <\p> [8] F. D. Natterer, F. Patthey and H. Brune, ACS Nano 8, 7099 (2014).<\p>