Synthesis and Characterization of Pd over Novel TiO2 Mixtures: Insights on Metal–Support Interactions

Abstract

Palladium nanoparticles were supported on unusual mixtures of anatase, TiO2 (II) and rutile titania phases by wet impregnation, obtaining catalysts with metal contents of ca. 0.25 wt % labeled Pd/Ti5, Pd/Ti45, and Pd/Ti120. Crystalline structures were confirmed by X-ray diffraction. Pd particle sizes in the range of 4-20 nm were observed by scanning-transmission electron Microscopy. External surface areas (SBET) in the range 10-17 m 2 g −1 were higher enough to achieve a good distribution of palladium over titanium oxide outer surface, as evidenced by energydispersive X-ray spectroscopy elemental profiles. Pd 0 /Pd δ+ atomic ratio measured by X-ray photoelectron spectroscopy showed a decrease from Pd/Ti5 to Pd/Ti120, in line with the decrease in anatase phase present in the catalysts. This behavior suggested that palladium tended to form more TiPdxO structures in Pd/Ti5 whilst PdOx structures were more likely to be present on supports with greater amounts of TiO2 (II) and rutile, due to the distinct metal-support interactions. An increase in reducibility and oxygen mobility from Pd/Ti5 to Pd/Ti120 was observed by temperature programmed measurements and associated to the different high-energy ball milled supports. Catalysts with improved properties reported herein could exhibit an excellent performance in oxidation reactions, e.g., glycerol selective oxidation.