Strong metal–support interactions on rhodium model catalysts

Abstract

Reactive processes on catalyst surfaces are studied in this work for Rh/metal oxide model systems by means of surface science techniques. Published results in the literature deal with titania, alumina, and silica as support materials and are briefly reviewed. For the present studies Rh/Al 2 O 3 and Rh/TiO 2 model catalysts with about one monolayer Rh coverage are specially prepared and analyzed by ion scattering spectroscopy, X-ray photoelectron spectroscopy, and thermal desorption measurements as main techniques. In part these measurements are supported by a variety of other analytical and imaging techniques. For thermal treatment in hydrogen atmosphere at low and elevated pressures a complete Rh encapsulation by titania is observed for temperatures above 773 K. The results from ion bombardment depth profiling are corroborated by the concomitant drastic reduction of the CO adsorption capacity of these samples. The model catalysts thus exhibit the typical features of 'strong metal-support interaction'. The effect was not found for alumina supports, for which thermal treatments mainly resulted in gradual interdiffusion of the various surface species. These results also demonstrate that characteristic catalyst behavior can be successfully studied by applying surface science methods to model catalysts.

Pd deposition on TiO2(110) and nanoparticle encapsulation

“…This is in contrast to Bennett et al 21,26 who showed the layer on Pd to be Ti 2þ -like by using take-off angle variations in XPS, though the effect on CO adsorption 27 was similar to that observed by Linsmeier and Taglauer. 25 Reactivity measurements by Bonanni 28 suggest that high-temperature annealing of Pt on reduced TiO 2 results in the encapsulation of Pt by a reduced titania layer, agreeing with a mechanism proposed by Fu et al…”

Enhanced Catalytic Hydrogenation Performance of Rh-Co2O3 Heteroaggregate Nanostructures by in Situ Transformation of Rh@Co Core–Shell Nanoparticles

“…The binding energy assignment is in accordance with those in the literature. 43−45 As shown in Figure 5a, the binding energies at 307.1/311.8 and 308.1/312.8 eV in Figure 5a can be ascribed to 3d 5/2 /3d 3/2 of metallic Rh and oxidized Rh 3+ species, respectively, while the binding energies at 778.1/793.1 and 780.3/795.8 eV could be assigned to 2p 3/2 /2p 1/2 of Co 0 and Co 3+ species, respectively. 46−48 In addition, a broad satellite peak at 783.6/802.0 eV is assigned to 2p 3/2 /2p 1/2 of Co 2 O 3 , suggesting that the Co ions are primarily in a high-spin electronic state.…”

Size-dependent activity of Pt/yttria-stabilized zirconia catalyst for ethylene and carbon monoxide oxidation in oxygen-free gas environment

“…Yoo et al [47] reported that as Pt NPs size decreases from 6 to 1 nm, there is stronger metalsupport interaction depicted from greater change in the electronic factors that cause the modification of the work function of the catalyst surface. Authors used the potential of zero total charge (PZTC) and in-situ X-ray absorption near-edge structure (XANES) to analyse the electronic states and show that small noble metal NPs in the range of 1.5 nm exhibit much higher changes in the electronic properties, which explains their high activity toward organic molecules oxidation [47][48][49]. Smallest NPs were also found to have higher surface coverage by oxygenated species promoted by TiO 2 than larger NPs [47].…”