Leveraging Conformational Dynamics of MOFs to Overcome Conversion‐Selectivity Trade‐Off in CO ₂ Hydrogenation to Ethanol

Abstract

ABSTRACT In this study, we exploit the structural dynamics of MIL‐53(Al) metal‐organic framework (MOF) to develop a highly efficient and selective aqueous‐phase heterogeneous catalyst, [MIL‐53‐Co(OH)], featuring atomically dispersed Co II (OH) active species at the MOF's nodes for the hydrogenation of CO 2 into ethanol. Under mild conditions (130°C, 20 bar, H 2 /CO 2 : 3), MIL‐53‐Co(OH) achieves 92% CO 2 conversion with an ethanol productivity of 10 133 µmol g cat −1 h −1 and 93% selectivity. Comparisons with the rigid MIL‐68(Al) and breathing‐suppressed variants of MIL‐53 MOFs revealed that the lattice flexibility of MIL‐53‐Co(OH) enhances ethanol productivity by at least 3.5‐fold while suppressing the formation of CH 3 OH. Experimental, structural and computational analysis suggest that the reversible narrow‐pore ( np )↔large‐pore ( lp ) interconversion of MIL‐53‐Co(OH) periodically optimizes the Al 2 [ μ 3 ‐O–Co(OH)] active‐site geometry at MOF's node, which synchronizes in situ generated CH 3 OH activation followed by CO insertion to promote C‒C coupling. During the np → lp transition, the transient lattice expansion relaxes the Al–[ μ 3 ‐O–Co(OH)]–Al hinge, which reduces the activation barrier of σ ‐bond metathesis between the Co–H bond and C–O bond of CH 3 OH, a key step in the catalytic cycle. This strategy of leveraging conformational dynamics of MOFs for active‐site engineering opens new avenues in designing highly active earth‐abundant metal catalysts for challenging chemical transformations.