Isocyanic acid (HNCO) dissociation on Rh(001) surface: A DFT study with and without dispersion correction

Abstract

The adsorption and coadsorption of CO and NH species, and the dissociation of HNCO molecule on the flat Rh(001) surface have been investigated using density functional theory (DFT) with GGA-PBE functional. Also, effect of van der Waals (vdW) dispersion correction, in particular the vdW-DF-revPBE variant is studied. The hollow site on the Rh(001) surface is found to be the most energetically stable for NH, while the bridge site is found for the CO as well as HNCO molecule. However, the inclusion of dispersion correction to the PBE changes the order of site preference for the CO while NH site preference remains the same. Also, the inclusion of vdW-DF-revPBE correction reduces the adsorption energy. Furthermore, the Climbing-Image Nudged Elastic Band (CI-NEB) method has been used to determine the minimum energy path for the molecular HNCO dissociation into NH and CO on the Rh(001) surface. We obtain an activation energy of 0.55 eV for the standard PBE, whereas the inclusion of vdW-DF-revPBE dispersion to the PBE functional results in activation energy of 0.51 eV. Our study therefore suggests that the rapid reduction of nitrogen oxide (RAPRENOx), a chemical combustion process designed to remove harmful NO from harmful combustor exhaust, is a high temperature process, if the Rh(001) is used as a reaction surface. Our analysis of electronic structures, in the form of projected density of states and electronic density, unravels the origin of HNCO molecular dissociation on the flat Rh(001) surface.