Title : Enhanced Catalytic Performance Of Sulphated TiO2-SiO2 by La Promoter for Butyl Glucoside Synthesis
Alkyl glucosides are non-ionic chemicals with excellent properties such as low toxicity and good biodegradability. They have attracted the interest of researchers due to their diverse applications as food emulsifiers, personal care products, cleaning agents, textile lubricants, drug carriers and antimicrobial agents. Alkyl glucosides are termed as green surfactants since they are synthesized using renewable carbohydrates and alcohols. Conventionally, homogenous acids such as mineral acids (HCl, HF, and H2SO4) and p-toluenesulfonic acid are used for the alkyl glucoside production. However, they suffer from problems related with waste recovery, environmental hazards, corrosion and difficulties in catalyst recovery and product purification. Heterogeneous catalysts improved the Fischer glycosidation, but there is a constant need to develop active, selective and reusable heterogeneous catalysts. Sulphated metal oxides might be considered as alternative solid acid catalysts due to their high acidity, high activity, easy separation and recyclability, but they have stability problems due to the surface sulphate leaching. Mixed oxides were studied to overcome this limitation, and they showed better activity and thermal stability than their constituent single oxide. Titania-silica mixed oxides have been extensively reported in the literature. Different methods have been developed for their synthesis such as co-precipitation, impregnation, flame hydrolysis, chemical vapour deposition, etc. Besides them, the sol-gel method has high potential for controlled surface properties by tuning the preparation conditions.
In this study, a series of La promoted sulphated TiO2-SiO2 catalysts were prepared by sol-gel with different La amounts and sulphate loading, as novel catalysts for this reaction. The effect of different La and sulphate amounts on the properties, activity and stability of the catalysts were investigated. Reaction temperature and catalyst amount were also studied as reaction parameters. The catalyst characterization was performed using N2 adsorption, XRD, XRF, NH3-TPD and pyridine adsorbed FTIR.
The results showed that, the acidity and the amount of Brønsted acid sites (B/L ratio) was enhanced with La and sulphate loading while the surface area and pore size decreased. The catalysts were tested in butyl glucoside synthesis. Catalytic activity changed depending on the acidity and the amount of Brønsted acid sites. The highest butyl glucoside yield (71.4 %) was obtained over S1/La4-TiO2-SiO2 catalyst which had the highest acidity and B/L ratio. Lower glucose conversion and butyl glucoside yield was obtained at lower reaction temperature. The initial butyl glucoside formation rate also decreased with reaction temperature. The increase in the catalyst amount caused a slight increase in both glucose conversion and butyl glucoside yield. No significant change was observed in the initial butyl glucoside formation rate. When the catalysts with different La amount were compared, it was found that the stability was improved with La addition. This proved that the La promoter enhanced the interaction between sulphate groups and TiO2-SiO2. The stability of the catalysts was proved by the results of the reusability tests.
- The study exhibit the synthesis method and performance test results of La promoted sulphated titania-silica mixed oxide catalysts with high surface area, mesoporous structure and high stability for the alkyl glucoside production.
- The details of the sol-gel synthesis procedure might be useful to develop mesoporous mixed metal oxides with high surface area and acidity. This type of catalysts are applicable for various acid catalyzed reactions.
- La promotion is proved to be an effective approach to prevent the sulphate leaching and to enhance the stability of the catalyst.
- The results of the study showed that the La promoted sulphated titania-silica mixed oxide catalysts are promising alternatives for the production of alkyl glucosides. Alkyl glucosides can be produced via more environmentally friendly process with the use of the heterogeneous catalysts prepared.