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

Abstract

: Palladium nanoparticles were supported on unusual mixtures of anatase, TiO 2 (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 (S BET ) 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 energy-dispersive 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 TiPd x O structures in Pd/Ti5 whilst PdO x structures were more likely to be present on supports with greater amounts of TiO 2 (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. inducing low-temperature reducibility and an increase in the mobility of reactive oxygen species, as evidenced by TPM analyses, factors well-known to benefit oxidation reactions. Present catalysts are being tested in liquid-phase glycerol selective oxidation in order to study the influence of metal– support interactions on the catalytic performance.