Pd-loaded modulated MOF-808: a bifunctional solid-acid catalyst for one-pot oxidation-acetalization

The growing demand for fine chemicals and environmental concerns have driven research interest in catalytic cascade processes that offer operational efficiency and high atom economy, though designing high-performance multifunctional solid catalysts remains a key challenge. This study demonstrates the rational design of a bifunctional Pd/MOF-808 catalyst for the one-pot tandem oxidation-acetalization of benzyl alcohol with ethylene glycol. Through defect engineering, MOF-808 variants were synthesized using different modulating agents to tailor their acidic properties. Structural characterization confirmed the preservation of MOF-808's microporous framework and revealed enhanced acidity in hydrothermally synthesized MOF-808-H₂O/HAc/HCl. Pd nanoparticles were immobilized via double-solvent impregnation, exhibiting high dispersion and electronic interaction with Zr-oxo clusters, as evidenced by XPS and TEM. The optimal Pd/MOF-808-H₂O/HAc/HCl achieved 99.9% benzyl alcohol conversion and 82.8% acetal selectivity, outperforming zeolite-supported Pd catalysts (HY, HZSM-5 and SAPO-11). While the oxidation rate was consistent across all catalysts, the MOF-808 support's optimal moderate acidity was crucial for directing selectivity toward acetalization and minimizing byproduct formation. The catalyst maintained its performance over six cycles without Pd leaching or structural degradation, highlighting the synergy between metallic sites for oxidation and tailored acidic sites for subsequent transformation in tandem catalysis.