Titania (TiO₂) is among the most efficient heterogeneous acid catalysts or supports employed so far for the production of commodity chemicals from lignocellulosic biomass in water.¹ The presence of fluorine in the TiO₂ matrix modifies its surface properties as well as its electronic structure, resulting in significant changes in its optical, electrical, acidic and catalytic properties.² In particular, the fluorine insertion can enhance the Lewis/Brønsted acidity of metal oxide materials due to the electron-withdrawing effects of fluorine atoms.³ Preparation of fluorinated metal oxides often uses HF, which is a high-risk reagent. This study proposes to prepare new fluorinated titania catalysts by innovative sol-gel method using new titania precursors containing either direct Ti-F bonds or fluorinated ligands. This strategy yields better control over the degree of fluorination, leading to tailored properties in the materials and improve reproducibility in the synthesis process.

  Newly synthesized molecular precursors, characterized thouroughly by FT-IR, NMR (¹H, ¹⁹F), TG-DTG studies and single crystal X-ray structure, were studied for sol-gel optimization to obtain nanometric fluorinated titania catalysts. Their controlled hydrolysis afforded mesostructured fluorinated TiO₂ with high F-contents (13-17%), which induced structural modifications in TiO₂ and changed its acid properties significantly. In this work we present the two representative fluorine doped titania samples F-1 and F-2 with 17.7 and 12.9% atomic fluorine content, respectively (as determined by the XRF analysis). As compared to the non-doped TiO₂, the XRD patterns of the samples F-1 and F-2 showed a slight shift in the peak positions of TiO₂, thus indicating successful incorporation of the fluorine atoms in the TiO₂ matrix. The N₂ adsorption/desorption isotherms show a typical type IV isotherms corresponding to the mesoporous materials, with F-1 showing the highest surface area of 390 m²/g (as compared to 280 and 250 m²/g for F-2 and undoped TiO₂, respectively). After structural analysis (N₂ ads/des, XRD, XPS, XRF) and acidity measurements by calorimetry of NH₃ adsorption, these catalysts were studied for their catalytic activity for the aqueous phase conversion of dihydroxy-acetone to Pyruvaldehyde/Lactic acid.

References

[1] E. Jolimaitre et al. Catal. Sci. Technol. 2018, 8, 1349–1356; A. B. S. Neto et al., Applied Catal. A: Gen. 2023, 658, 119165.

[2] S. Celerier, F. Richard, Catal. Commun. 2015, 67, 26.

[3] E. Kemnitz, Catal. Sci. Technol. 2015, 5, 786