The interaction of CO molecules on Au–Rh bimetallic nanoclusters supported on a thin film of Al₂O₃/NiAl(100)

Abstract

The interaction of CO molecules adsorbed on Au-Rh bimetallic nanoclusters supported on an ordered thin film of Al 2 O 3 /NiAl(100) was studied, primarily with infrared reflection absorption spectroscopy and densityfunctional-theory calculations. The bimetallic clusters, grown by sequential deposition of vapor Au and Rh onto the Al 2 O 3 /NiAl(100) surface at 300 K, had diameters of 1.2-3.0 nm and heights of 0.4-1.2 nm; they had a fcc phase and grew in the orientation (100). The infrared absorption line for CO adsorbed on Au sites (CO Au ) of the bimetallic clusters at 110 K was narrow (centered about 2100 cm À1) and intense, which results largely from the small adsorption energy and large dipole moment of CO Au , whereas that on Rh sites (CO Rh ) was broad (1880-2100 cm À1) and weak, which contrasts also with its counterpart on pure Rh clusters. Upon increasing the temperature to remove CO Au , the absorption line for CO Rh narrowed and the intensity increased; at 300 K, the line width decreased by 30-40% and the absorption intensity was enhanced by 40-60%. The former arose, after the desorption of CO Au , from a decreased CO-CO interaction and inhomogeneous broadening; the latter corresponded to an enhanced dipole moment of CO Rh , attributed to a promoted charge transfer from the CO Rh -binding Rh to the neighboring Au and consequently increased charge donated from CO Rh to Rh. The varied IR absorption for adsorbed CO can thus serve as an indicator for the charge transfer between the components in bimetallic clusters.

Decomposition of methanol-d4 on Rh nanoclusters supported by thin-film Al2O3/NiAl(100) under near-ambient-pressure conditions

“…3 and 5) were modeled with a round-shaped Rh cluster ( Rh C ) and a Rh(100) surface ( Rh(100) ), respectively. 17,50,66,67,69 As the H 2 O*, introduced by the increased pressure, 33 could dissociate into hydroxyl (OH*) on Rh surfaces, OH*-decorated Rh cluster and Rh(100) surface, denoted as Rh C-OH and Rh(100) OH , respectively, were modeled to investigate the methanol reactions under NAP conditions (Fig. 6a).…”

“…, the adsorbate effect. 69 Additionally, the dissociation of CO* had a greater E a and was more endothermic Δ E on Rh C-OH (3.58 and 0.78 eV) than on Rh(100) OH (2.74 and 0.53 eV), attributable to the more crowded charge distribution of C* + O* co-adsorbed on the small Rh C-OH , i.e. , the lateral effect, 64 as shown in Fig.…”

Au–Rh Surface Structures on Rh(111): DFT Insights into the Formation of an Ordered Surface Alloy

“…[18][19][20][21][22][23][24][25][26][27][28][29] In a number of studies Au and Rh were sequentially evaporated by physical vapor deposition (PVD) on oxide single crystalline surfaces. 18,19,21,22,28,29 When first Au nanoparticles were prepared on a rutile TiO 2 (110) surface followed by evaporation of Rh, an efficient place exchange already occurred at room temperature, leading to the incorporation a great part of Rh atoms into the subsurface of Au clusters, while the outermost layer still mostly consisted of gold. 18 The driving force for this process is the smaller surface energy of Au compared to that of Rh (1.283 J/m 2 for Au(111) and 2.472 J/m 2 for Rh(111)).…”

“…The combination of these metals proved to be beneficial in visible-light-induced hydrogen generation from water, , in the electrochemical oxygen evolution reaction, in selective hydrogenation of cinnamaldehyde, as well as in the hydroconversion of tetralin . The mixing and segregation properties of these metals restricted to the nanoscale were previously studied in detail. − In a number of studies Au and Rh were sequentially evaporated by physical vapor deposition (PVD) on oxide single crystalline surfaces. ,,,,, When first Au nanoparticles were prepared on a rutile TiO 2 (110) surface followed by evaporation of Rh, an efficient place exchange already occurred at room temperature, leading to the incorporation of a great part of Rh atoms into the subsurface of Au clusters, while the outermost layer still mostly consisted of gold . The driving force for this process is the smaller surface energy of Au compared to that of Rh (1.283 J/m 2 for Au(111) and 2.472 J/m 2 for Rh(111)) .…”

“…19 A similar behavior was revealed for Au and Rh on Al 2 O 3 /NiAl(100). 28,29 Au−Rh bimetallic nanoparticles were also prepared by applying wet chemical methods, in some cases combined with reductive or oxidative gas treatments to obtain catalysts. These investigations revealed a clear tendency for phase separation in accordance with the bulk immiscibility of these metals.…”