LOW-TEMPERATURE PHOTOASSISTED GENERATION OF A STRONG METAL SUPPORT INTERACTION IN A RH/TIO2 CATALYST

UV irradiation (lambda > 300 nm) of suspensions of a Rh/TiO2 catalyst precursor containing Rh3+ in an i-PrOH/H2O mixture leads to the generation of small metallic particles (d < 1.5 nm by TEM). Using H-2 adsorption, it has been found that a strong metal-support interaction (SMSI) is developed in this irradiated Rh/TiO2 precursor when it is reduced with hydrogen at a low temperature (i.e., 473 K), a situation that is normally observed only after reduction at 773 K in samples prepared from nonirradiated precursors. Structural modifications, characterized by a binding energy (BE) shift of ca. -0.5 eV of the Rh(3d) peak, were observed by XPS in the samples prepared from the irradiated precursor and in all the samples reduced at 773 K. From the H-2 adsorption, XPS, and TEM data, it has been concluded that atomic hydrogen, evolved at the in situ photogenerated Rh metallic particles, deeply reduces the TiO2 support in the neighborhood of the particles generating oxygen vacancies which favor a better Rh-TiO2 electronic interaction and the setup of the SMSI state under milder conditions (i.e., H-2 at 473 K).