H2 reactivity on Pd/Cu and Pd/Ru bimetallic surface alloys

MAXIMILIANO RAMOS ACEVEDO; MARINA MINITTI; CRISTINA DÍAZ; DANIEL FARÍAS; RODOLFO MIRANDA; FERNANDO MARTÍN; ALEJANDRA ELISA MARTÍNEZ; HERIBERTO FABIO BUSNENGO

Postdam

Workshop; 2nd International Workshop on Scattering of Atoms and Molecules from Surfaces; 2013

Bimetallic surface alloys offer a wide variety of technologically relevant properties, i.e., selectivity, tuneable reactiveness, control over the product/surface binding energy. These features are closely related to the modifications in the electronic structure of a given surface metal atom due to interactions with different neighbors, and the strain effects imposed by the lattice mismatch of the host and guest materials. Particularly, alloys containing Pd as guest material on different substrates have attracted the interest in the last years from both the experimental [H. Hartmann et al, Surface Science 603, 1439?1455 (2009),A. E. Baber et al, Chem. Cat. Chem. 02155, 1?9 (2010)] and theoretical sides [A. Gross, Topics in Catalysis 37, 29?39 (2006)]. Among these substrates, Cu(111) and Ru(0001), already known to be in opposite sides about their reactivity to hydrogen are very good candidates in order to compare the changes introduced by Pd alloying. Small amounts (~1%) of Pd deposited on Cu(111) have proved to turn on the reactivity of the this otherwise inert surface. On the other hand, Pd deposition seems to have no effect on Ru(0001) surface: the reactivity remains constant, until the Pd concentration reaches high values (greater than ~95%) when the H2 sticking probability sharply drops down two orders of magnitude. In order to understand the striking features observed in the dissociative adsorption process taking place in both bimetallic surfaces, we present a theoretical characterization of the most relevant features of the Potential Energy Surface for H2+PdCu/Cu(111) and H2+PdRu/Ru(0001). Minimum energy pathways corresponding to selected configurations and their comparison with the pure metal surfaces ones are also included. Local density of states are analysed for each case as well as estimations of the sticking coefficient based on molecular dynamics (QCT and AIMD) calculations for both systems. New measurements of H2 sticking probability on PdCu/Cu(111) and PdRu/Ru(0001) obtained using Hellium Atom Scattering are also included.