Mechanistic assessments of acetaldehyde aldol condensation under capillary condensation within defective Zr-MOFs

Chain-growth reactions of light biomolecules are crucial for green chemical processes, among which Guerbet reactions involving acetaldehyde intermediates stand out. This study examines the selective aldol condensation of acetaldehyde towards crotonaldehyde using UiO-66 MOFs modulated with benzoic acid, which highlights the performance over other modulators. Detailed spectroscopic data and DFT simulations reveal unreported catalytically active species. Surface μ 1 -OH groups are identified as critical active sites for aldol condensation, in synergy with Zr⁴⁺ Lewis acid centers. High selectivity (>90 %) is achieved through the desorption of bound products facilitated by the presence an extended capillary liquid. These findings at low conversion conditions enhance into the understanding of active sites and the capillary effects in defective Zr-MOFs, providing insights for upgrading relevant biomolecules. • UiO-66 activity is boosted by increasing the number of μ 1 -OH/H 2 O pairs in cluster. • μ 1 -OH groups are new catalytically active species for aldol condensation reaction. • Capillar condensation provides an improved selectivity towards desired product.