Binding of propene on small gold clusters and on Au(111): Simple rules for binding sites and relative binding energies

Abstract

We use density functional theory(DFT) to investigate the bonding of propene to small gas-phase gold clusters and to a Au(111) surface. The desorption energy trends and the geometry of the binding sites are consistent with the following set of rules.(1) The bond of propene to gold is formed by donation of electron density from the highest occupied molecular orbital (HOMO) of propene to one of the low-lying empty orbitals [denoted by LUMO1, LUMO2, … (LUMO-lowest unoccupied molecular orbital)] of the gold cluster. (2) Propene binds to a site on the Au cluster where one of the low-lying LUMOs protrudes in the vacuum. Different isomers (same cluster, but different binding sites for propene) correspond to sites where different low-lying LUMOs protrude in space. (3) The desorption energy of the lowest energy isomer correlates with the energy of the lowest empty orbital of the cluster; the lower the energy of that LUMO, the higher the desorption energy. (4) If the lowest-lying LUMO protrudes into space at two nonequivalent sites at the edge of a cluster, propene binds more strongly to the site with the lowest coordination. These rules are consistent with the calculated bond energies and geometries for [Aun(C3H6)]q, for n=1−5 and n=8 and q=−1, 0, +1. Based on them we have made a number of predictions that have been confirmed by DFT calculations. The bond of propene to gold is strengthened as the net charge of the cluster varies from −1, to zero, to +1. Compared to a gas-phase cluster, a cluster on a support binds propene more strongly if the support takes electron density from the cluster (e.g., a Au cluster on a goldsurface) and more weakly if the support donates electron density to the cluster (e.g., a Au cluster on an oxygen vacancy on an oxide surface). KeywordsGold, Binding sites, Density functional theory, Desorption, Oxide surfaces Disciplines Chemistry CommentsThe following article appeared in Journal of Chemical Physics 121 (2004) We use density functional theory ͑DFT͒ to investigate the bonding of propene to small gas-phase gold clusters and to a Au͑111͒ surface. The desorption energy trends and the geometry of the binding sites are consistent with the following set of rules. ͑1͒ The bond of propene to gold is formed by donation of electron density from the highest occupied molecular orbital ͑HOMO͒ of propene to one of the low-lying empty orbitals ͓denoted by LUMO1, LUMO2, ... ͑LUMO-lowest unoccupied molecular orbital͔͒ of the gold cluster. ͑2͒ Propene binds to a site on the Au cluster where one of the low-lying LUMOs protrudes in the vacuum. Different isomers ͑same cluster, but different binding sites for propene͒ correspond to sites where different low-lying LUMOs protrude in space. ͑3͒ The desorption energy of the lowest energy isomer correlates with the energy of the lowest empty orbital of the cluster; the lower the energy of that LUMO, the higher the desorption energy. ͑4͒ If the lowest-lying LUMO protrudes into space at two nonequivalent sites at the edge of a cluster, propene binds more strong...

Mechanistic Study into the Direct Epoxidation of Propene over Gold/Titania Catalysts

“…7 The attention to these catalysts has not diminished, as is evidenced by the number of reports published by many groups over the last year. [8][9][10][11][12][13][14][15][16][17][18][19][20] Despite all of this attention, the mode of operation of these catalysts is still under discussion, especially for the epoxidation of propene. Both gold and titania seem to be a necessity for a catalyst to be able to epoxidize propene.…”

Density functional study of the adsorption of propene on mixed gold-silver clusters, AunAgm: Propensity rules for binding

“…In two previous papers 1,2 we have studied the adsorption of propene on small Au and Ag clusters. We have found there a number of ''empirical'' rules that allow us to guess the relative desorption energy and the binding site of the propene, from the shape and the energy of the lowest unoccupied molecular orbital ͑LUMO͒ of the ''naked'' metal cluster.…”

Theoretical study of the adsorption of H on Sin clusters, (n=3–10)

“…5 where it can be observed that the maximum of the Fukui function is always in the positions where the hydrogen atom binds. It seems that the f Ff ± is, in part, a quantitative application of the rules proposed by Chrétien et al 21,22 Next, it is important to assess the quality of the obtained results. Therefore, the total energy and the binding energy per atom, BE= ͓E͑Si n H͒ − nE͑Si͒ − E͑H͔͒ / n, of all the clusters have been calculated using the already presented B3LYP/ 6-311+ + G ** , the LSDA/ 6-311+ + G ** , and the MP2 / 6-311+ + G ** methodologies.…”

“…19 Galvan et al have studied the reactivity of Si 4 with a single atom ͑Si or Ga͒ 20 using the reactivity indices defined in the density-functional theory ͑DFT͒. The topology of the frontier orbitals were used by Chrétien et al 21,22 to propose simple rules which can be used to predict the binding site of propene to Au and Ag clusters. Mañanes et al 23 have used the topology of the Fukui function and the atomic condensed Fukui function analysis to study the bonding and reactivity of H and Al 13 clusters.…”