FTIR study of the photo-induced reaction of NO + CO on Rh/TiO2

Abstract

The effect of UV illumination on the stability of Rh dicarbonyl on TiO₂ and on the surface interaction of NO + CO gas mixture on TiO₂ and Rh/TiO₂ catalysts was examined with FTIR spectroscopy. Photolysis of Rh¹(CO)₂ over TiO₂ caused the decomposition of this complex, and the formation of Rh_x–CO and Rh₂(CO)₃ surface compounds. Illumination of the NO + CO/TiO₂ system at 200 K produced a new band at 2212 cm⁻¹, which is attributed to the Ti–NCO species. This species is not observed in the absence of illumination even after extended adsorption time. Coadsorption of NO + CO gas mixture on Rh/TiO₂ gave an absorption band at 2160–2175 cm⁻¹, not detected after adsorption of NO and CO separately. This band is assigned to the vibration of NCO bonded to the Rh. UV illumination dramatically enhanced the surface concentration of Rh–NCO surface species at both 200 and 300 K. It is assumed that the extent of the electron transfer from TiO₂ to the Rh is enhanced due to the photoelectrons which leads to the greater probability of the surface dissociation of NO, the key step in the formation of NCO surface complex.