(745e) Molten Salt Hydrates As Solvents in the Synthesis of Metal Oxide Catalysts

Metal oxides, a large family of materials, unambiguously play an important role either as dispersed active phase or as stable supports in heterogeneous catalytic systems. These materials are very attractive due to their unique physicochemical properties such as high surface area, crystallinity, redox properties, thermal stability, acid-base functionality etc. (1). Transition metal oxides such as titanium dioxide (TiO₂), are utilized as catalysts in several reactions including oxidation, dehydration and dehydrogenation reactions due to their low cost of production, ease of regeneration, catalytic reactivity/selectivity/stability (1). Among TiO₂ crystal phases, Anatase has attracted interest, especially as catalyst supports due to its higher than Rutile surface area as well as better metal-support interactions (2). Synthesizing stable Anatase at high temperature has been reported to be desirable also for antibacterial material applications but usually Anatase transforms to rutile between 600^oC and 700^oC (4). Several approaches have been reported to improve the thermal stability of Anatase including the sulfuric acid and Molten Salts (MS) routes (3)(4). Although both methods lead to improved materials, due to the highly corrosive synthesis environment as well as high operation temperature, alternative routes should be considered.

This study investigates a simple method to synthesize Anatase-TiO₂ using different synthesis precursors and Molten Salt Hydrates (MSH) as the reacting solvent system. In this method, precursors such as titanium isopropoxide (TTIP) and titanium n-butoxide (TNB) undergo hydrolysis and condensation reaction within the ordered structure of molten salt hydrates thus modifying the morphology of TiO₂ particles. The solvent can be almost fully recovered simply by filtration. The reaction (synthesis) as well as calcination temperature have been examined in order to show their effects on the morphology, crystal structure, surface and uniformity of TiO₂ crystals. Synthesized materials are characterized using different techniques such as Raman spectroscopy, Scanning Electron Microscopy and BET surface area measurements. Results of this study show the formation of unique structure of Anatase-TiO₂ with surface area as high as 230 m²/g. The crystallinity of the prepared materials is improved at high calcination temperature without sacrificing significantly their morphology. In-situ Raman calcination data will be discussed, in an effort to unravel the effect of calcination temperature and time on the molecular structure, crystallinity and morphology of the final catalysts.

References

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2) Bagheri, S., Julkapli, N., & Hamid S. (2014). Titanium Dioxide as a Catalyst Support in Heterogeneous Catalysis. The Scientific World Journal, 2014. Article ID 727496, 21

3) Mao, Y., Park, T., Zhang, F., Zhou, H., & Wong, S. S. (2007). Environmentally Friendly Methodologies of Nanostructure Synthesis. ChemInform,38(41). doi:10.1002/chin.200741212

4) Periyat, P., Pillai, S. C., Mccormack, D. E., Colreavy, J., & Hinder, S. J. (2008). Improved High-Temperature Stability and Sun-Light-Driven Photocatalytic Activity of Sulfur-Doped Anatase TiO2. The Journal of Physical Chemistry C,112(20), 7644-7652. doi:10.1021/jp0774847