Theoretical study of CO oxidation by Cu, Ag and Au nanoparticles and extended surfaces

G.S. OTERO; B. PASCUCCI; P.G. BELELLI; F. ILLAS; M.M. BRANDA

Congreso; XXXIX Congreso Internacional de Químicos Teóricos de Expresión Latina (QUITEL); 2013

XXXIX Congreso Internacional de Químicos Teóricos de Expresión Latina (QUITEL)

Metallic nanoparticles are increasingly used in almost all the fields of science and technology. These systems exhibit physical and chemical properties which are significantly different from those of the bulk and of perfect, extended, surfaces. In this work, the reactivity and geometrical properties of Cu19, Ag19 and Au19 nanoparticles and of the corresponding (111) surface has been evaluated with a periodic density functional theory (DFT) based approach using the Vienna Ab-Initio Simulation Package (VASP). The DFT based calculations were carried out using the PW91 generalized gradient approach form of the exchange-correlation potential using a plane wave basis set and with the projector augmented-wave (PAW) method to take into account the effect of core electrons in the valence electron density. The (111) surfaces were simulated by the repeated slab model using 2 × 2 supercells and including four metallic layers in the slab. The co-adsorption of CO and O on the nanoparticles and (111) surfaces was explored by considering all possible combination of surface sites. The CO2 adsorption on different sites of nanoparticles and surfaces were also performed. The CO + O co-adsorption is more favorable on the Cu and Au nanoparticles than on respective (111) surfaces, as expected, while the co-adsorption energy values are similar for Ag nanoparticle and Ag(111). The site preferred for the CO adsorption on all nanoparticles is on-top of corner atoms. Besides, some stable sites for CO + O co-adsorption are obtained for the Cu(111) and Au(111) surfaces and also for the respective nanoparticles, but, so far, this is not observed on Ag. The energy values for the CO oxidation reaction (CO + O → CO2) are more exothermic on Cu and Ag nanoparticles than on the corresponding (111) surfaces. Preliminary results indicate that the reaction energy is similar for Au19 and Au(111).