Controlling the Synergistic Role of Pd and Defective UiO-66 for Alcohol Chain Growth via Guerbet Pathways

The catalytic upgrading of short-chain alcohols into higher-value products is a key step toward sustainable fuel synthesis, with the Guerbet reaction offering a direct pathway to long-chain alcohols. In this study, Pd-modified UiO-66 materials are examined to clarify how Pd species and framework functionalities cooperate to control catalytic activity, product selectivity, and catalyst stability. Operando characterization and DFT calculations show that H2 pretreatment generates finely dispersed Pd0 nanoparticles (Pd0 NPs), while a fraction of Pd remains in ionic form associated with linker-defective Zr clusters and undergoes partial migration under reaction. Catalytic evaluation reveals that low Pd contents favor the selective 1-butanol formation by limiting ethanol dehydration, whereas higher Pd loadings lead to nanoparticle growth, site isolation, and reduced catalytic efficiency. The results indicate that the optimal Guerbet performance relies on the functional complementarity between Pd0 sites, which enable hydrogen transfer, and framework μ-OH and Zr acid sites that drive acetaldehyde coupling. These findings demonstrate that the careful control of defect density and metal incorporation in UiO-66 allows efficient ethanol chain growth with high Guerbet selectivity (>90 %) and stable performance in the absence of external H2, highlighting the promise of MOF-based catalysts for renewable fuel production.