Direct Synthesis of Cyclic Carbonates by Oxidative Carboxylation of Styrenes over Ti-Containing Catalysts
The mesoporous titanium-silicate Ti-MMM-E prepared by the simple and affordable evaporation-induced self-assembly
methodology demonstrated superior catalytic performance in terms of substrate conversion and carbonate selectivity in the oxidative carboxylation of styrenes with the environmentally benign oxidant, tert-butyl hydroperoxide, in the presence of tetrabutylammonium bromide cocatalyst at mild reaction conditions (50-70 oC, 8 bar CO2). Ti-MMM-E showed superior catalytic performance as compared to other types of mesoporous and microporous Ti-containing catalysts, including the metal-organic framework MIL-125. Under green solvent-free conditions, the selectivity towards styrene carbonate reached 68 and 70 % at 72 and 92 % substrate conversion at 50 and 70 oC, respectively. The volume yield of styrene carbonate as high as 0.3 kg per L of the reaction mixture could be achieved. Importantly, no titanium leaching into solution occurred and the Ti-MMM-E catalyst could be easily recycled and used repeatedly with maintenance of the catalytic properties.