SPECTROSCOPIC STUDIES ON ADSORPTION STATES OF IRON PENTACARBONYL ADSORBED ON TITANIUM-DIOXIDE

The adsorption states and reactivity of Fe(CO)5 adsorbed on TiO2 (anatase) have been studied by FT-IR and UV-Vis diffuse reflectance spectroscopy. When a TiO2 sample with a large surface area (50 m2 g-1) is outgassed at temperatures above 373 K, adsorbed Fe(CO)5 exhibits a marked increase in the amount of adsorption, a significant red shift of IR bands in the C-O stretching region, and a new absorption band in the visible region. These phenomena are not observed on the TiO2 Sample oxidized in O2 at 673 K followed by outgassing at room temperature. The surface of TiO2 thus provides different kinds of adsorption sites for Fe(CO)5 depending on its oxidation state. When the adsorbed Fe(CO)5 on TiO2 is exposed to NO, a substitution reaction of the carbonyl ligands with NO readily occurs at room temperature, whereas no such reaction takes place on silica and alumina. These results are discussed in terms of the electronic interaction between adsorbed Fe(CO)5 and the electron-donating sites of the substrate.