Mesoporous Melamine-Formaldehyde Resins as Efficient Heterogeneous Catalysts for Continuous Synthesis of Cyclic Carbonates from Epoxides and Gaseous CO2

Herein, we report the application of inexpensive mesoporous melamine-formaldehyde resins (MMFR and MMFR250) obtained by a novel template-free and organosolvent-free hydrothermal method as efficient heterogeneous catalysts for direct synthesis of cyclic carbonates from CO(2 )and epoxides (epichlorohydrin, butylene oxide, and styrene oxide). The catalytic activities of the melamine resins were attributed to the abundant Lewis basic N-sites capable of activating CO2 molecules. Based on CO2-temperature programmed desorption, ;organosohretit-f,ec the concentrations of surface basic sites for MMFR and MMFR250 were estimated to be 172 and 56 mu mol/g, while the activation energies of CO2 desorption (strength of basic sites) were calculated to be 92.1 and 64.5 kJ/mol. We also observed considerable differences in the catalytic activities and stabilities of polymeric catalysts in batch and in continuous-flow mode due to the existence of a synergism between adsorption of CO2 and cyclic carbonates (poison). Our experiments also revealed the important role of catalyst surface chemistry and CO2 partial pressure upon catalyst poisoning. Nevertheless, owing to their unique properties (large specific surface area, large mesoporous, and CO2 basicity), melamine resins presented excellent activities (turnover frequency 207-2147 h(-1)) and selectivities (>99%) for carbonation of epoxides with CO2 (20 bar initial CO2 or CO2:epoxide mole ratio similar to 1.5) under solvent-free and co-catalyst-free conditions at 100- 120 degrees C. Most importantly, these low-cost polymeric catalysts were reusable and demonstrated exceptional stability in a flow reactor (tested up to 13 days of time on stream, weight hourly space velocity 0.26-1.91 h(-1)) for continuous cyclic carbonate production from gaseous CO(2 )with different epoxides (conversion 76-100% and selectivity >99%) under industrially relevant conditions (120 degrees C, 13 bar, solvent-free/co-catalyst-free) confirming their superiority over the previously reported catalytic materials.