Increased Back-Bonding Explains Step-Edge Reactivity and Particle Size Effect for CO Activation on Ru Nanoparticles

• DOI: 10.1021/jacs.6b08697
• Publication Date: 2016-11-30T08:13:28Z
• Authors: Lucas Foppa; Christophe Copéret; Aleix Comas-Vives
• Keywords: Reactivity; Particle (ecology)

Carbon monoxide is a ubiquitous molecule, key feedstock and intermediate in chemical processes. Its adsorption activation, typically carried out on metallic nanoparticles (NPs), are strongly dependent the particle size. In particular, small NPs, which principle contain more corner step-edge atoms, surprisingly less reactive than larger ones. Hereby, first-principles calculations explicit Ru NP models (1-2 nm) show that both large NPs can present sites (e.g., B5 B6 sites). However, such display strong particle-size-dependent reactivity because of very subtle differences local bonding. State-of-the-art crystal orbital Hamilton population analysis allows detailed molecular picture adsorbed CO step-edges, be classified as flat (η1 coordination) concave (η2 sites. Our shows π-metal dπ hybrid band responsible for electron back-donation better represented by an oxygen lone pair sites, whereas it delocalized C O atoms increasing back-bonding these compared to step-edges or low-index surface The bonding also rationalizes why cleavage easier ones irrespective site geometry. lower due smaller extent Ru-O interaction η2 mode, destabilizes transition-state structure direct cleavage. findings provide understanding consistent with observed size effect.