Selective structural transformation of metal-organic frameworks for hydrogenation reaction

The structure transformation of metal-organic frameworks (MOFs) is significant for expanding the MOF family and exploring new MOF properties; however, it remains a significant challenge. In this work, we showcase the structure transformation of an Hf-based MOF. This MOF, with different phases denoted as Hf-SDC(face-centered cubic (fcc)) and Hf-SDC(hexagonal close-packed (hcp)), was successfully synthesized under controlled synthesis conditions. Interestingly, we demonstrated that the obtained two different phase MOFs can be further transformed to amorphous Hf-SDC-Br(am) and semi-crystalline Hf-SDC-Br(sc) through a simple bromination reaction, which converts the rigid –C=C– bonds into flexible –C(Br)–C(Br)– bonds. Specifically, the three-dimensional fcc topology could no longer be maintained, and the interlayer order of the hcp topology was disrupted, resulting in the amorphous Hf-SDC-Br(am) and semi-crystalline Hf-SDC-Br(sc), respectively. Finally, as a proof-of-concept application, the semi-crystalline Hf-SDC-Br(sc) was used as a support to load with Pd nanoparticles, yielding a Pd/Hf-SDC-Br(sc) catalyst. Benefiting from the Br-Pd interaction and the retained partial structural order that facilitates mass transport of reactants, Pd/Hf-SDC-Br(sc) exhibited excellent catalytic performance in the conversion of vanillin to 2-methoxy-4-methylphenol, with a record turnover frequency of 1021 h⁻¹. This work demonstrates the feasibility of the structure transformation of MOF through simple chemical reaction and highlights the importance of the structure transformation of MOFs for advanced catalysis.