The role of surface-molecule energy exchange on the reactivity of O2 on Cu_ML/Ru(0001)

MAXIMILIANO RAMOS ACEVEDO; CRISTINA DÍAZ; ALEJANDRA ELISA MARTÍNEZ; FERNANDO MARTÍN; HERIBERTO FABIO BUSNENGO

Madrid

Workshop; 16th Workshop on Dynamical Phenomena at Surfaces; 2014

Bimetallic surfaces are becoming very attractive for surface scientists due to their great practical interest. Very often they present chemical properties significantly different from those of their parent metals [1-3]. Thus, they can be used, for instance, to enhance selectivity in some catalytic processes, such as transition metal oxidation ones. To shed some light and get more insight into such processes, we have studied the dissociative and non-dissociative adsorption of O 2 on Cu ML /Ru(0001). STM experiments [4] have shown that sticking coefficients for O 2 on a monolayer (ML) of Cu adsorbed on Ru(0001) is almost three order of magnitude larger than those of clean Cu(111). It has been suggested that this behavior may be due to the presence of a empty surface state in the electronic structure of Cu_ML=1/Ru(0001). On the other hand, subsequence King and Wells (KW) measurements [5] have shown that sticking coefficients for Cu_ML=1/Ru(0001) are less than an order of magnitude larger than those of Cu(111), for incidence energies above 0.2 eV. Our theoretical adiabatic simulations, using accurate six-dimensional potential energy surfaces (PES), reveal that KW measured sticking coefficients for O2/Cu_ML=1/Ru(0001) are due to both dissociative adsorption and molecular adsorption. Our simulations also show that the inclusion of surface atoms motion is fundamental to reproduce qualitatively the experimental results. Eventually, our first results on O2/Cu_ML=2/Ru(0001) show sticking coefficients similar to those obtained by STM measurements. Our results on this system seem to indicate that a surface state is not the responsible for the decrease of the sticking coefficients as function of the number of Cu layers, because the surface state is not well reproduced in our calculations. [1] Schalapka et al Phys. Rev. Lett. 91, 016101 (2003) [2] Xu et al J. Am. Chem. Soc. 126, 4717 (2004) [3] Kibler et al Angew. Chem. Int. Ed. 44, 2080 (2005) [4] Otero et al Surf. Sci. 550, 65 (2004) [5] Minniti et al J. Chem. Phys. 137, 074706 (2012)