Rational fabrication of ordered porous solid strong bases by utilizing the inherent reducibility of metal-organic frameworks

Ordered porous solid strong bases (OPSSBs) have attracted great research interest due to the excellent performance as heterogeneous catalysts in various reactions. The main obstacle for fabricating OPSSBs is the requirement of high temperature to produce strong basicity on ordered porous materials. For example, the temperatures of 600–650 °C are required for the decomposition of base precursor NaNO₃ to basic sites on mesoporous silica SBA-15 and zeolite Y. Such high decomposition temperatures are energy-intensive and harmful to the structure of supports. Herein, we report the fabrication of OPSSBs by utilizing the redox interaction between base precursor and low-valence metal centers (e.g., Cr³⁺) in metal-organic frameworks (MOFs). The base precursor NaNO₃ on MIL-101(Cr) can be converted to basic sites entirely at 300 °C, which is quite lower than those of the conventional thermal conversion on SBA-15 and zeolite Y (600–650 °C). The exploration on decomposition mechanism reveals that the valence change of Cr³⁺ to Cr⁶⁺ takes place during the conversion of NaNO₃ to basic sites. In this way, MOFs-derived base catalysts have been synthesized successfully by the host–guest redox strategy and exhibit high catalytic activity in typical base-catalyzed reactions.