PHOTOASSISTED DEPOSITION OF RHODIUM ON PLATINUM TITANIA SAMPLES AS A METHOD OF PREPARING BIMETALLIC CATALYSTS

Rh-Pt/TiO2 samples obtained by UV illumination at room temperature in the absence of oxygen of suspensions in aqueous Rh3+ solutions of particulate 2.5 wt.-% Pt/TiO2 (previously prepared by impregnation and reduction in hydrogen), were examined by X-ray photoelectron spectroscopy and transmission and scanning transmission electron microscopy. Depending on the medium (water, 2-propanol-water, ammonia solution buffered at pH 11 with ammonium chloride or nitrate), rhodium particles (ca. 1 wt.-% loading) of various mean size and degree of reduction were found. Interestingly, rhodium was deposited on titania in neutral medium and on platinum in basic medium. These results, which demonstrate that different types of bimetallic catalysts can be prepared by photoassisted deposition, are discussed in terms of the separation of photoproduced charges and surface charge. © 1990.