Hydrophobicity Boosts Catalytic Activity: The Tailoring of Aluminosilicates with Trimethylsilyl Groups

Introducing organic groups into metal silicate catalysts and thus supposedly changing the surface hydrophobicity has been shown to enhance the catalyst performance in various reactions. However, the organic groups introduction does not unambiguously guarantee hydrophobicity control. Therefore, a thorough characterization is necessary to provide a complete view of the interaction between the catalyst surface, reactants, and products. Herein, an aluminosilicate catalyst with well-dispersed Al atoms was prepared via the non-hydrolytic sol-gel method. This material was post-synthetically modified with trimethylsilyl groups; their number on the catalyst surface was controlled via a temperature-vacuum pretreatment. In such a way, aluminosilicate materials with similar porosity, structure, and acid site strength and quality were obtained. Notably, the water sorption measurements showed that trimethylsilylated aluminosilicates adsorb 2.5-3 times less water than the parent material (p/p(0)=0.3). The turn-over-frequency in epoxide ring opening and ethanol dehydration scaled up with the number of trimethylsilyl groups grafted on the catalyst surface. Particularly, the heavily trimethylsilylated sample achieved three to five times higher turnover-frequency in styrene oxide aminolysis than the parent aluminosilicate material. To the best of the authors' knowledge, it exhibited the most active Al sites for epoxide aminolysis in the present literature.

Automated summary

Introducing organic groups into metal silicate catalysts can improve their performance, but it does not guarantee hydrophobicity control. Thorough characterization is necessary to understand the interaction between the catalyst surface, reactants, and products. In this study, an aluminosilicate catalyst was modified with trimethylsilyl groups, and the number of groups was controlled. Water sorption measurements showed decreased water adsorption, and the turnover frequency in certain reactions increased with the number of trimethylsilyl groups.