Architecturally Defined Node Vacancies and Defect Pairs in MIL-100(Al) Catalyze Propene-Selective 2-Propanol Dehydration: Structural Insights from Probe-Molecule Analysis

The metal–organic framework MOF MIL-100(Al) offers a structurally well-defined platform for investigating how node architecture, including defects, governs catalysis. Using 2-propanol dehydration as a probe reaction, we elucidated catalytic behavior by varying the ligand environments on the MIL-100 Al 3 O nodes. NMR and infrared spectra and dynamic performance of the catalyst show that selective propene formation originates from the cooperation of two distinct node-site motifs: adjacent (a) vacancy sites capable of binding alcohol and alkoxide species and (b) defect Al–Al pair sites bearing bridging hydroxo groups. The hydroxo groups on Al–Al defect sites are critical in enforcing total selectivity to propene by blocking condensation pathways between neighboring alcohol and alkoxide ligands, thereby suppressing di-isopropyl ether formation. The suppression of ether formation is a defining characteristic of the MIL-100 node structure, as demonstrated by the emergence of ether products when the framework is partially degraded by high-temperature treatments, generating alumina-like domains. The results demonstrate how precisely defined, quantifiable active sites intrinsic to MOF nodes enable mechanistic clarity not attainable for conventional, structurally heterogeneous metal oxide catalysts. The results highlight MIL-100(Al) as a tunable material platform for probing structure–reactivity relationships in oxide-containing catalysis.