Study elucidates mechanism of MOF-mediated catalysis

In addition to garnering widespread attention as materials for gas storage and separation, metal-organic frameworks (MOFs) have shown themselves to be worthy catalysts in a limited number of reactions. MOFs’ catalytic usefulness could be boosted by design, if researchers understood how these crystalline porous materials drive reactions. But many details remain unknown. So a team led by Christopher J. Cramer and Laura Gagliardi of the University of Minnesota, Twin Cities, and Bruce C. Gates of the University of California, Davis, coupled spectroscopy and computational methods to ferret out mechanistic details of a test reaction—ethanol dehydration on the MOFs UiO-66 and UiO-67 (J. Am. Chem. Soc. 2018, DOI: 10.1021/jacs.7b13330). These MOFs contain Zr₆O₈ clusters joined by dicarboxylic acid linkers. Because MOF clusters function as catalysts when they have defects—for example, vacancies due to missing linkers—the researchers deliberately introduced vacancies synthetically. Analysis of the resulting MOFs shows that they dehydrate ethanol selectively, forming diethyl ether, not ethylene, the competing product. The team notes that the key to selectivity is having adjacent vacancies, which enables ethanol molecules to bind to neighboring sites on the clusters and facilitates ether formation via an S_N2 mechanism.

CORRECTION: This story was updated March 20, 2018, to correct Bruce C. Gates’s affiliation. He is a professor at the University of California, Davis, not the University of California, Irvine.