Synergy of Paired Bronsted-Lewis Acid Sites on Defects of Zr-MIL-140A for Methanol Dehydration

As a common defect-capping ligand in metal-organicframeworks(MOFs), the hydroxyl group normally exhibits Bronsted acidityor basicity, but the presence of inherent hydroxyl groups in the MOFstructure makes it a great challenge to identify the exact role ofdefect-capping hydroxyl groups in catalysis. Herein, we used hydroxyl-freeMIL-140A as the platform to generate terminal hydroxyl groups on defectsites via a continuous post-synthetic treatment.The structure and acidity of MIL-140A were properly characterized.The hydroxyl-contained MIL-140A-OH exhibited 4.6-fold higher activitythan the pristine MIL-140A in methanol dehydration. Spectroscopicand computational investigations demonstrated that the reaction wasinitiated by the respective adsorption of two methanol molecules onthe terminal-OH and the adjacent Zr vacancy. The dehydration of theadsorbed methanol molecules then occurred in the Bronsted-Lewisacid site co-participated associative pathway with the lowest energybarrier.