Effects of Alumina Thickness on CO Oxidation Activity over Pd₂₀/Alumina/Re(0001): Correlated Effects of Alumina Electronic Properties and Pd₂₀Geometry on Activity

Abstract

The CO oxidation activity of size-selected Pd 20 clusters deposited on alumina films grown on Re(0001) is shown to depend strongly on the film thickness in the 0 to 10 nm range. For the reaction conditions of these experiments, binding and activation of O 2 is shown to be the limiting process, which can be varied by a factor of 2 by tuning the alumina film thickness, due to effects on both the electronic structure of the alumina film and the morphology of the supported Pd clusters. The alumina films are shown to be doped with Re atoms diffusing from the Re(0001) substrate, leading to a strong dependence of the surface electronic properties on alumina thickness, which in turn, results in the observed thickness-dependent activity of the Pd 20 .

From two- to three-dimensional alumina: Interface templated films and formation of γ−Al2O3 (111) nuclei

“…Similar concepts also apply to molecules adsorbed on insulating ultrathin films: The gap between the highest occupied and lowest unoccupied molecular orbital as well as the charge transfer upon adsorption depend not only on polarization effects at the interface, but to a large extent also on the thickness of the insulating layer [9][10][11]. Catalytic activity can also change drastically in such systems: Recently, it was shown that due to changes in the electronic properties, the CO oxidation activity of palladium clusters deposited on alumina (Al 2 O 3 ) films on Re(0001) strongly depends on the film thickness [12]. To fully understand which properties of the adsorbed species rely on the adsorbate/oxide interface and which are influenced by the underlying substrate material, the oxide thickness needs to be varied in a controlled manner [13].…”

Controlling Ethylene Hydrogenation Reactivity on Pt13 Clusters by Varying the Stoichiometry of the Amorphous Silica Support

“…Model catalysis on supported transition-metal particles under ultrahigh-vacuum (UHV) conditions allows precise control of critical factors that govern heterogeneously catalyzed reactions,t hereby reducing the complexity of the system and allowing targeted investigations of key parameters influencing the reaction activity,selectivity,and specificity of acatalyst. [1][2][3] To date,UHV studies have shown the ability to influence the chemical and/or morphological properties of nanoparticles supported on thin metal oxide films [4] by controlling the precise particle size, [5][6][7][8][9] the film thickness, [10][11][12][13][14][15] the presence of defect sites, [4,6,16] and the reduction state of the thin film. [17] Acommonly used support in heterogeneous catalysis is a-SiO 2 , [18,19] and it has been shown that a-SiO 2 thin films grown in UHV provide an opportunity to vary the metal oxide stoichiometry through selection of the growth parameters.…”

Selective Growth of Al2O3 on Size-Selected Platinum Clusters by Atomic Layer Deposition

“…5a, no 13 with Pt in this temperature range. On the other hand, we have also observed CO desorption in this temperature range for defective alumina films grown on single crystal supports, [42,45,46] thus the sites exposed by annealing may simply be defects in the alumina.…”