CO-induced structural changes of supported Rh promoted by NO Original Research Article

The effects of NO on the CO-induced structural changes of Rh deposited on SiO2, MgO and TiO2 are investigated in the temperature range 110–503 K by means of infrared spectroscopy. It was observed that the addition of NO to CO dramatically enhanced the development of gem-dicarbonyl, RhI(CO)2, from Rhx—CO species — indicative of the occurrence of the oxidative disruption of the Rhx cluster — for all the three samples at 233–300 K. This is explained by the formation of a strong bond between NO and Rhx crystallites which weakens the Rh—Rh bond. It is assumed that the NO and its dissociation product, the adsorbed O, participate in the oxidation of isolated Rh0 atoms to RhI ions. On the other hand, the presence of NO slowed down the conversion of gem-dicarbonyl into Rhx—CO at and above 448 K to a great extent, indicating that NO retards the reductive agglomerization of RhI to Rhx crystallites on these supports.