Mild Vacancy Generation and Acidification of the H-USY Zeolite with a Single-Electron Organic Donor.

The ultra-stabilized acidic Y (H-USY) zeolite is a robust, microporous, tridimensional, crystalline aluminosilicate widely employed as a solid catalyst in petrochemistry and fine chemistry, in virtue of its acidity and high internal surface area. Here we show that these two parameters, i.e., acidity and internal surface area, are enhanced when the H-USY zeolite is treated with a single-electron organic donor such as thianthrene, without any additional solvent nor additive. A spontaneous electron donation from thianthrene to the zeolite framework occurs, to generate the corresponding thianthrene cation radical and the negatively charged zeolite, which, counterintuitively, increases rather than decreases the zeolite acidity, after generating vacancies in the zeolite framework and increasing the surface area. The vacant H-USY solid (vac-H-USY) catalyzes the opening reaction of epoxides with alcohols and water with nearly twice faster reaction rates compared to the pristine H-USY, and the solid is recoverable and reusable. These results bring a mild and green methodology to generate vacancies in zeolites, circumventing current methodologies at >400 °C, and also to increase the surface area and acidity of the solid zeolite without altering neither its structure nor metal composition, with applications in catalysis and beyond.