An unexpected pathway for the catalytic oxidation of methylidyne on Rh{111} as a route to syngas

This study investigates the adsorption properties of methylidyne (CH) on Rh{111}, its partial and full oxidation as well as its surface mobility, by means of plane-wave density functional theory (DFT) calculations. Besides investigating known oxidation pathways on rhodium, such as decomposition of CH and subsequent oxidation of the decomposition products, new pathways such as direct reaction of methylidyne and oxygen toward a surface aldyhyde-type species and the decomposition of this species are considered. The unexpected and novel pathway determined here by DFT is utilized for a microkinetic model of the formation of CO and CO2 from methylidyne. A comparison of this microkinetic study with experimental data shows that our novel mechanism can indeed describe the observations. This comparison strongly suggests that this new alternative route is the main reaction pathway for the conversion of methylidyne.     

Linear relationship between activation energies and reaction energies for coverage-dependent dissociation reactions on rhodium surfaces

Evidence of a relationship between activation energies and enthalpy changes of various dissociation reactions on transition metals has been reported recently. A reconsideration of density functional theory results for dissociation energies of oxygen and NO on different rhodium surfaces (low-index and stepped) and their dependencies on oxygen precoverage reveal that also here a linear Br?nsted-Evans-Polanyi (BEP) relationship exists. The establishment of such a general concept would be of tremendous importance for the development of detailed, elementary-step reaction mechanisms, because the activation energies of reaction steps as well as their coverage dependencies could be estimated based on the adsorption energies calculated by means of DFT.