Oxidation of carbidic carbon on a rhodium surface

Abstract

Different mechanisms of atomic carbon and oxygen recombination on a rhodium surface are studied with Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The kinetics of adsorbed carbidic carbon oxidation (carbon coverage 0c ~ 0.1-0.3 ML) by gas-phase oxygen that proceeds by a Langmuir-Hinshelwood reaction mechanism, provides the value of the activation energy for recombination (Ea: t g 170 -4-20 kJ/mol). Erae et depends slightly on the carbon coverage. An Eley-Rideal type of reaction was observed for adsorbed oxygen and atomic gas-phase carbon recombination which occurs in a dynamic regime. The low value found for the activation energy (near zero) is consistent with the mechanism that this exothermic reaction is too fast for energy dissipation into the substrate; the energy is mainly transferred into translational, vibrational and rotational energy of CO.

Heterogeneous Combustion of Benzene on Rh(111): Kinetics and Dynamics of CO and CO2 Production

“…We can therefore extract a value of the activation energy for the reaction of adsorbed C and O independent of assumptions about O , while quantifying the value of the preexponential factor is beyond the scope of our numerical analysis. The average value for the three reaction conditions used is ∼130 kJ/mol, which is smaller than that previously reported for polycrystalline Rh(170 kJ/mol) (18) and Ni(100) (179 kJ/mol) (33); both of these studies were done at higher carbon coverages. Furthermore, carbon on rougher facets of the polycrystalline surface may be more highly coordinated to the rhodium surface and hence more tightly bound compared to carbon on the Rh(111) surface currently under investigation.…”

“…We assign an activation energy of E a = 130 kJ/mol to the surface reaction of carbon and oxygen. This value is somewhat lower than the higher coverage ( C = 0.2 ML) value on polycrystalline rhodium of 170 ± 20 kJ/mol (18). This variation may result from attractive interactions between carbon atoms at higher coverage which hinder reaction.…”

“…Mikhailov (18) demonstrates a mild trend of this sort in an investigation of oxidation of carbon on a polycrystalline rhodium ribbon. The observed activation energy varied from 168 kJ/mol at C = 0.1 ML to 185 kJ/mol at C = 0.5 ML.…”

Time‐Resolved, In Situ DRIFTS/EDE/MS Studies on Alumina‐Supported Rhodium Catalysts: Effects of Ceriation and Zirconiation on Rhodium–CO Interactions

“…[22, 23] The CO dissociation process taking place on relatively small Rh nanoparticles (less than 3 nm) is also a source of the oxidative disruption of Rh particles. [24, 25]…”

“…[22,23] The CO dissociation process taking place on relativelys mall Rh nanoparticles (less than 3nm) is also as ource of the oxidative disruption of Rh particles. [24,25] Because modern TWCs are composed of precious-metal particles (e.g. Rh, Pt, Pd) and variouso xide materials, such as CeO x and ZrO 2 ,t ypically supported on Al 2 O 3 , [8,9] it is important to understandt he effects of these components on CO interactions.…”