Unraveling the synergistic role of Pd and defective UiO-66 for ethanol Guerbet reaction

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 guide the catalytic activity and product selectivity whilst promoting the catalyst stability. Operando characterization and DFT calculations reveal that: (I) H 2 pretreatment generates finely dispersed Pd 0 nanoparticles (Pd 0 NPs). In parallel, (II) a secondary fraction of Pd remains in ionic form occupying the linker-defective positions near the zirconium oxo-clusters of the framework, and (III) that palladium ions undergo partial migration during the reaction. Catalytic evaluation reveals that low Pd loadings promote selective 1-butanol formation by suppressing ethanol dehydration, whereas higher Pd loadings induce nanoparticle growth, active-site agglomeration, and diminished catalytic efficiency. All in all, optimal Guerbet performance relies on the complementarity of Pd 0 sites, which enable hydrogen transfer, and framework μ-OH and Zr acid sites that drive acetaldehyde coupling. These findings establish that precisely balancing linker defectivity and Pd loading in UiO-66 is key to achieving efficient ethanol chain growth, outstanding Guerbet selectivity (>90%), and stable operation without external H 2 , underscoring the potential of MOF-based catalysts for sustainable fuel production.