Preparation of Ga2O3 Doped Sulfonated Tin Oxides as a Highly Active and Recyclable Heterogeneous Solid Acid Catalyst for Aldol Reactions

Ga₂O₃ doped sulfonated tin oxide catalysts were prepared via co-condensation method in ethanol solvent, followed by sulfonation and calcination. The samples were characterized by isothermal nitrogen adsorption/desorption, powder X-ray diffraction (XRD), thermal gravimetric analysis (TG), Raman spectra and DRIFT spectra. The number of acid sites on the catalysts was measured with the potentiometric titration of butyl amine. The results showed that the addition of small amounts of Ga₂O₃ to sulfonated tin oxide resulted in an enhanced acid site density, which makes Ga₂O₃ doped sulfonated tin oxide catalysts highly active for aldol reactions. The catalyst containing 1.5% Ga₂O₃ exhibited much higher activity than those of SO₄²-/SnO₂, SO₄²-/ZrO₂ and H₃PO₄ in aldol condensation of prenal and prenol for citral precursor, which is a important in fragrance industry. Besides the high activity, the catalyst also exhibited good recyclability, making 1.5% GST an efficient and promising solid catalyst for aldol reactions.