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Synthesis and Characterization of Pd over Novel TiO2 Mixtures: Insights on Metal-Support Interactions
* 1 , 2 , 3 , 1 , 1
1  Instituto de Investigaciones en Tecnología Química (INTEQUI-CONICET), Universidad Nacional de San Luis (UNSL), Facultad de Química Bioquímica y Farmacia, Almirante Brown 1455, Capital, 5700 San Luis, Argentina
2  Departamento de Ingeniería y Ciencia de los Materiales y del Transporte, Escuela Politécnica Superior, Universidad de Sevilla, Virgen de África 7, 41011 Sevilla, Spain
3  Instituto de Ciencia de Materiales de Sevilla, (CSIC-Univ. Sevilla), Avda. Américo Vespucio 49, 41092 Sevilla, Spain


Palladium nanoparticles were supported on unusual mixtures of anatase, TiO2 (II) and rutile titania phases (not commercially available) by wet impregnation, obtaining catalysts with metal contents of 0.25 wt% labeled Pd/Ti5, Pd/Ti45 and Pd/Ti120. Crystalline structures were confirmed by X-Ray Diffraction (XRD) and Raman Spectroscopy. Pd loadings were quantified by Inductively Coupled Plasma (ICP-OES) whilst particle sizes in the range 4-20 nm were obtained by Transmission Electron Microscopy (TEM). Low-values of external surface area (SBET) in the range 10-17 m2 g-1, measured by Brunauer-Emmet-Teller (BET) method, were higher enough to achieve a good distribution of palladium over titanium oxide outer surface, as evidenced by Energy-Dispersive X-ray Spectroscopy (EDS) elemental mapping. Pd0/Pdδ+ atomic ratio measured by X-Ray Photoelectron Spectroscopy (XPS) 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 phases, 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 (TPM), which could be associated to the different defective structures achieved in the supports previously synthesized by high-energy ball milling. Catalysts with improved properties reported herein could exhibit an excellent performance in oxidation reactions, e.g. liquid-phase glycerol selective oxidation.

Keywords: Titanium oxide; palladium; supported catalysts; metal-support interactions