“…At submonolayer coverages of Au, the desorption peak is centered at 1310−1320 K. For Au/Rh(111) surfaces the Au−substrate bond is weaker (by ∼4 kcal/mol 36 ) than for Au/Mo(110) surfaces, and in Figure the separation between the desorption temperatures of the multilayer and monolayer states is relatively small. These trends are in agreement with the results of previous studies that show an increase in the strength of the Au−substrate bonding interactions when going from late- to early-transition metal substrates . On Rh(111), the adsorption bonds of Au and S are weaker than on Mo(110).…”
Section: Resultssupporting
confidence: 92%
“…The metal clusters shown in Figure were used to model the adsorption of Au and S on hollow and a-top sites of Mo(110) and Rh(111). Previous studies indicate that clusters of this size provide the basic interactions that occur during the adsorption of atoms and small molecules on metal surfaces. ,38d Since they cannot be used to study long-range interactions between adsorbates on a surface, we will focus our attention on short range Au ↔ S interactions and how Au and S affect the electronic properties of the nearest-neighbor substrate atoms. 13 Clusters used to model the interaction of Au and S with Mo(110) and Rh(111).…”
The coadsorption of Au and S on Mo(110) and Rh(111) has
been examined using thermal desorption mass
spectroscopy, photoemission, and ab initio self-consistent-field
calculations. On both surfaces, the interactions
between Au and S are repulsive. S reduces the adsorption energy of
Au. In some cases, the weakening of
the Mo−Au and Rh−Au bonds is so large (5−7 kcal/mol) that the Au
adatoms “ball up” on the surface
instead of “wetting” the Mo(110) and Rh(111) substrates.
The ab initio SCF calculations show that a S
adatom modifies the chemical behavior of adjacent Mo and Rh sites by
reducing their contribution to the
density of states around the Fermi level of the system, weakening in
this way their ability to form strong
bonds with Au. In the Au/S/Mo(110) and Au/S/Rh(111)
surfaces, Au and S compete for the electrons of the
transition-metal substrate. Gold produces dramatic changes in the
reaction pathways for the removal of sulfur
from the Mo and Rh surfaces. In the Au/S/Rh(111) system,
S2 desorbs at much lower temperatures (100−250 K) than in S/Rh(111). For Au/S/Mo(110), the presence
of Au favors desorption of S2 instead of
migration
of S into the bulk of Mo. These results are consistent with a
model in which Au compresses the S overlayer
into islands of high local coverage, reducing in this way its stability
and favoring the “pairing” of sulfur
atoms and desorption of S2.
“…At submonolayer coverages of Au, the desorption peak is centered at 1310−1320 K. For Au/Rh(111) surfaces the Au−substrate bond is weaker (by ∼4 kcal/mol 36 ) than for Au/Mo(110) surfaces, and in Figure the separation between the desorption temperatures of the multilayer and monolayer states is relatively small. These trends are in agreement with the results of previous studies that show an increase in the strength of the Au−substrate bonding interactions when going from late- to early-transition metal substrates . On Rh(111), the adsorption bonds of Au and S are weaker than on Mo(110).…”
Section: Resultssupporting
confidence: 92%
“…The metal clusters shown in Figure were used to model the adsorption of Au and S on hollow and a-top sites of Mo(110) and Rh(111). Previous studies indicate that clusters of this size provide the basic interactions that occur during the adsorption of atoms and small molecules on metal surfaces. ,38d Since they cannot be used to study long-range interactions between adsorbates on a surface, we will focus our attention on short range Au ↔ S interactions and how Au and S affect the electronic properties of the nearest-neighbor substrate atoms. 13 Clusters used to model the interaction of Au and S with Mo(110) and Rh(111).…”
The coadsorption of Au and S on Mo(110) and Rh(111) has
been examined using thermal desorption mass
spectroscopy, photoemission, and ab initio self-consistent-field
calculations. On both surfaces, the interactions
between Au and S are repulsive. S reduces the adsorption energy of
Au. In some cases, the weakening of
the Mo−Au and Rh−Au bonds is so large (5−7 kcal/mol) that the Au
adatoms “ball up” on the surface
instead of “wetting” the Mo(110) and Rh(111) substrates.
The ab initio SCF calculations show that a S
adatom modifies the chemical behavior of adjacent Mo and Rh sites by
reducing their contribution to the
density of states around the Fermi level of the system, weakening in
this way their ability to form strong
bonds with Au. In the Au/S/Mo(110) and Au/S/Rh(111)
surfaces, Au and S compete for the electrons of the
transition-metal substrate. Gold produces dramatic changes in the
reaction pathways for the removal of sulfur
from the Mo and Rh surfaces. In the Au/S/Rh(111) system,
S2 desorbs at much lower temperatures (100−250 K) than in S/Rh(111). For Au/S/Mo(110), the presence
of Au favors desorption of S2 instead of
migration
of S into the bulk of Mo. These results are consistent with a
model in which Au compresses the S overlayer
into islands of high local coverage, reducing in this way its stability
and favoring the “pairing” of sulfur
atoms and desorption of S2.
“…Due to the hybridization of the 6s, 6p, and 5d orbitals in bulk gold, it has an electron configuration of [Xe]4f 14 5d 10Àx 6s 1+x . 30,[32][33][34][35] Thus there are holes in the d band and a small white line appears. 20,29,36 The FT features an intense peak at 2.5 A ˚, due to the 12 Au neighbors at 2.85 A ˚.…”
Section: Reference Compoundsmentioning
confidence: 99%
“…The observed increase in the white-line intensity is due to the increasing extent of s-p-d hybridization with increasing cluster size. 30,[32][33][34][35] 3.3.5 Storage. The Au/TiO 2 precursor reduced under influence of light, as was readily observed by the change of the color from light yellow to lilac.…”
Incipient-wetness impregnation of gamma-Al(2)O(3) with HAuCl(4) and subsequent removal of chlorine with NaOH, and deposition-precipitation of HAuCl(4) on TiO(2) at pH 7 resulted in supported Au(3+) species. Time-resolved in situ XAS at the Au L(3) edge showed that the Al(2)O(3)-supported oxidic or hydroxidic species were reduced in hydrogen at 440 K to yield small metallic gold clusters. The Au(3+) precursor decomposed to metallic gold in inert atmosphere at 573 K and in oxidizing atmosphere above 623 K. In all atmospheres, initially small clusters were formed that gradually grew with increasing temperature. The TiO(2)-supported species were considerably less stable. In hydrogen and carbon monoxide, Au(0) clusters of 1 to 1.5 nm were formed at room temperature, which was the lowest temperature studied. In inert and oxidizing atmosphere, the Au(3+) precursor decomposed fully to metallic gold at 530 K, as shown by XAS and temperature-programmed experiments. Large clusters were obtained already in the initial stage of reduction. Residual chlorine inhibited the reduction and led to sintering of the gold clusters. Exposure of the TiO(2)-supported catalyst precursor to light or the X-ray beam led to partial reduction, and STEM showed that storage of the reduced gold clusters under ambient conditions led to agglomeration and bimodal cluster-size distributions.
“…With respect to the ruthenium complexes used in homogeneous catalysis, surface‐bound methoxy could only be formed on the metal if strong σ donor and weak π acceptor ligands were used to create an electron‐rich ruthenium center 11d. 25 An explanation for the higher catalytic activity of the Ru‐npAu‐material would thus involve a transfer of electron density from the gold substrate to the ruthenium,26 similar to the action of ligands in homogeneous ruthenium catalysts.…”
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