Synergistic Effects of Lewis Acid–Base Pair Sites─Hf-MOFs with Functional Groups as Distinguished Catalysts for the Cycloaddition of Epoxides with CO<sub>2</sub>
Lianlian Wang, Wan‐Zhen Qiao, Han Liu, Shuwen Li, Jie Wu, Hongwei Hou
Abstract
The incorporation of Lewis acid–base sites in catalysts has been considered as a significant approach to fabricating bifunctional catalysts with efficient catalytic activity for CO 2 fixation. In this paper, a series of Hafnium-based metal–organic frameworks (Hf-MOFs), NU-912(Hf) and NU-912–X(Hf)–X (X = −NH 2, −Br, −CN, and −I) derivatives assembled by Lewis acidic Hf 6 (μ 3 –O) 4 (μ 3 –OH) 4 (H 2 O) 4 (OH) 4 (Hf 6 ) clusters and Lewis base-attached organic linkers, are successfully synthesized by a facile ligand functionalization method. These isostructural Hf-MOFs, which exhibit diamond channels of 1.3 nm diameter, great chemical stability, and CO 2 adsorption capacity, have been evaluated as catalysts for the CO 2 cycloaddition reaction with epoxides. Catalytic experiments reveal that the micropore environments of these MOFs have an outstanding impact on catalytic activity. Remarkably, NU-912(Hf)–I serves as an efficient heterogeneous catalyst for this catalytic reaction under mild conditions due to the high density of Lewis acid Hf 6 cluster centers and strong Lewis base functional groups, surpassing most of the reported MOF-based catalysts.