A stable nanotubular metal-organic framework as heterogeneous catalyst for efficient chemical fixation of CO2

The incorporation of high-density and easily accessible Lewis acid sites is of great significance to obtain high catalytic activity in the CO2 cycloaddition reaction of epoxides. Nanotubular metal-organic frameworks (NTMOFs) have attracted widespread attention as heterogeneous catalysts because of their outstanding porosity, intriguing structural diversity and accessible active sites. However, NTMOFs used as heterogeneous catalysts are limited, mainly due to the synthetic difficulties and lack of chemical and physical stability. Herein, we constructed novel NTMOFs with an interior channel diameter of 1.8 nm and an exterior wall diameter of 3.0 nm. They exhibited excellent chemical resistance to both acid and alkaline solutions. The NTMOFs feature durable catalytic performance for CO2 cycloaddition with epoxides at atmospheric pressure with good recyclability. The turnover frequency (TOF) (306 h(-1)) value is greater than any previously reported value for metal-organic framework (MOF)-based catalysts for the cycloaddition of CO2 to epoxides under similar conditions. Experimental results and theoretical calculations reveal that the abundant coordinatively unsaturated open metal sites within the mesoporous nanotubular channels facilitates the sufficient contact of the catalytic active sites with the epoxide substrates, thus enhancing catalytic activity. More importantly, the new materials could be extended to CO2 fixation by the use of raw power plant flue gas.