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

Abstract

We use density functional theory to investigate the binding of propene to small mixed Au-Ag clusters, in the gas phase. We have found that the rules proposed by us for propene binding to Au and Ag clusters, also work for binding to mixed Au-Ag clusters. The rules state that propene binds to those sites on the edge of the cluster where the equal density plots of the LUMO of the naked cluster protrude into the vacuum. Furthermore, the desorption energy of propene correlate with the LUMO energy: the lower the LUMO energy, the stronger the propene bond. We have also found an additional rule that is specific to mixed clusters. We call active the atoms on which the LUMO of the naked cluster protrude in the vacuum, and inactive those for which such protrusions do not exist. To define the rules we use the following notation: A is an active site to which propene is bound B is another active site, and C is an inactive site. If the atom in C(Ag or Au) is replaced with another atom (Au or Ag) propene desorption energy changes very little. If we replace the atom B with a more electronegative atom (i.e., we replace Ag by Au) the propene bond to A becomes stronger. If we replace the atom B with a less electronegative atom (i.e., we replace Au by Ag) the propene bond to A becomes weaker. We use density functional theory to investigate the binding of propene to small mixed Au-Ag clusters, in the gas phase. We have found that the rules proposed by us for propene binding to Au and Ag clusters, also work for binding to mixed Au-Ag clusters. The rules state that propene binds to those sites on the edge of the cluster where the equal density plots of the LUMO of the naked cluster protrude into the vacuum. Furthermore, the desorption energy of propene correlate with the LUMO energy: the lower the LUMO energy, the stronger the propene bond. We have also found an additional rule that is specific to mixed clusters. We call active the atoms on which the LUMO of the naked cluster protrude in the vacuum, and inactive those for which such protrusions do not exist.To define the rules we use the following notation: A is an active site to which propene is bound B is another active site, and C is an inactive site. If the atom in C ͑Ag or Au͒ is replaced with another atom ͑Au or Ag͒ propene desorption energy changes very little. If we replace the atom B with a more electronegative atom ͑i.e., we replace Ag by Au͒ the propene bond to A becomes stronger. If we replace the atom B with a less electronegative atom ͑i.e., we replace Au by Ag͒ the propene bond to A becomes weaker.

A density functional theory study on the Ag n H (n = 1–10) clusters

“…The studies on the adsorption behavior of Ag and Cu clusters can provide important information to better understand the catalytic process of Ag-and Cu-based nanocatalysis. In fact, there are some studies on the adsorption behavior of O 2 , NO, CO, NCO, and C 3 H 6 onto small Ag clusters [15][16][17][18][19][20][21][22][23][24]. Kim et al [15] have studied the formation of di-oxygen species on Ag anion clusters by using the vibrationally resolved ultraviolet photoelectron spectroscopy and provide the evidence that O 2 can be adsorbed molecularly onto Ag anion clusters consisting of less than 15 atoms.…”

Density Functional Study of Molecular Hydrogen Adsorption on Small Gold–Copper Binary Clusters

“…In recent years, bimetallic metal clusters have attracted considerable attention both experimentally and theoretically primarily because they often exhibit distinct physical and chemical properties from the pure clusters [12][13][14][15]. The theoretical studies of the adsorption and reaction of H 2 on bimetallic clusters have also appeared [16][17][18][19][20].…”

Binding Interactions and Raman Spectral Properties of Pyridine Interacting with Bimetallic Silver–Gold Clusters

“…For example, the NÀM bond distances are in the range 2.163-2.278 for pyridine binding to the obtuse site, and 2.327-2.606 for pyridine binding to the acute site, which agrees well with the cases of pyridine binding to Ag 4 and Au 4 with a rhombic geometry. [32] A shorter bond distance in the obtuse case than the acute case must arise from the fact that the proper accepting LUMO in a rhombic cluster mainly populates along its short axis, [13,32,47] which means both atoms at the short axis should be the active sites for the bonding of pyridine.…”

“…For inorganic or organic molecules binding to the gold-silver clusters, the chemical bonding depends strongly on the property of the unoccupied orbital in the metallic cluster. [12,13] Mitric et al studied the catalytic oxidation of CO and O 2 adsorbed on mixed silver-gold clusters with respect to the role of CT in the catalytic activity of AgAu À . [2] Chretien et al studied the adsorption of propene on mixed gold-silver clusters.…”

“…[2] Chretien et al studied the adsorption of propene on mixed gold-silver clusters. [13] However, the understanding of spectroscopic properties from the influence of binding interactions between bimetallic clusters and organic molecules remains ambiguous.…”