Organic-inorganic hybrid mesoporous titanium silica material as bi- functional heterogeneous catalyst for the CO_2 cycloaddition

摘要

A kind of mesoporous titanium silica material containing polydiallyldimethylammonium chloride (PDDA) is synthesized by a facile hydrothermal method. The as-synthesized materials are determined by XRD, SEM, UV-Vis, FT-IR, TGA, CO2-TPD, organic elemental analysis and N-2 adsorption-desorption. The N-2 adsorption-desorption isotherms of the amorphous titanium silica materials are type IV curves, suggesting that materials possess mesoporous structure. Moreover, the PDDA not only is used as a "porogen" but also takes the function of basic active center and activates carbon dioxide (CO2). The CO2-TPD analysis is used to characterize the existence of basic sites and calculate the amount of accessible basic sites in the samples. The calculation results show that the basicity of the material increases with the enhanced amount of PDDA. The mesoporous titanium silica material contains two kinds of active centers simultaneously, which is highly active in fixation reaction of CO2 without co-catalyst. Finally, the epichlorohydrin (ECH) conversion could reach 96.5% and the cyclic carbonate selectivity is 95.0% under optimal conditions. It is worth noting that the amorphous mesoporous titanium silica material shows a superior catalytic performance comparing to Ti-mordenite with regular crystal structure and morphology. Meanwhile, the hybrid mesoporous catalyst shows good reusability and stability in the cycloaddition reaction.