Propene epoxidation with O-2 or H-2-O-2 mixtures over silver catalysts: theoretical insights into the role of the particle size

The adsorption and dissociation of molecular O-2 over silver extended surfaces, nanoparticles and clusters of different size, as well as the reaction between adsorbed O-2 and H-2 to form less nucleophilic hydroperoxide groups have been investigated by means of periodic DFT calculations. Hydroperoxide formation from O-2 and H-2 is in all systems kinetically favoured over O-2 dissociation, which becomes energetically forbidden on small planar clusters. The nature and reactivity towards propene of all oxygen species present on silver, including adsorbed molecular O-2, atomic O, and hydroperoxide groups, have been theoretically explored. Formation of the oxametallacycle intermediate involved in propene epoxidation is energetically accessible on subnanometric three-dimensional silver nanoparticles, but competitive pathways leading to hydrogen abstraction and allyl formation always involve lower activation barriers. Theoretical findings have been experimentally confirmed by Raman spectroscopy of O-2 adsorption and catalytic testing of planar and three dimensional silver clusters.The authors thank the Spanish Science and Innovation Ministry (MAT2011-28009, Consolider Ingenio 2010-MULTICAT, CSD2009-00050 and Severo Ochoa) for financial support, and Red Espanola de Supercomputacion (RES) and Centre de Calcul de la Universitat de Val'ncia for computing facilities and technical assistance. A. P. thanks the Spanish Science and Innovation Ministry (Juan de la Cierva program) for her grant.Boronat Zaragoza, M.; Pulido, Á.; Concepción Heydorn, P.; Corma Canós, A. (2014). Propene epoxidation with O-2 or H-2-O-2 mixtures over silver catalysts: theoretical insights into the role of the particle size. Physical Chemistry Chemical Physics. 16(48):26600-26612. doi:10.1039/c4cp02198cS2660026612164