Important interactions in the de-NOx process by quantum chemical approach

Density functional calculations were performed on Rh and Pd nitrosyl complexes (cluster calculations) and on MgO (100) supported Rh nitrosyl complex (periodic calculations) in order to model the metal-ligand bonding in the de-NOx catalytic processes. We found that the Rh atom can form stronger bond with the NO molecule than the Pd atom which results in a weaker N-O interaction in the RhNO complex. The calculated vibrational spectra and the metal-nitrogen interaction energies also supported this observation. The simple Blyholder model is employed to describe the nature of the metal-nitrosyl binding. The periodic calculations showed that the MgO (100) supported Rh atom can further elongate the N-O bond which means a larger activation effect. Comparison of the Rh-N interaction in the cluster and the periodic model of RhNO shows a slightly longer metal-ligand bond together with a somewhat smaller interaction energy. (author)