Defect-engineered halloysite nanotubes anchored with ultrafine Pd nanoparticles for enhanced catalytic hydrogenation of phenol

A novel defect-engineered strategy was developed to fabricate highly efficient Pd catalysts for the selective hydrogenation of phenol to cyclohexanone. By fine-tuning the post-alkali treatment, we successfully tailored the microstructure of halloysite nanotubes (HNTs) supports, selectively removing Al–OH sites without forming any amorphous structures. This precise engineering allowed for the uniform dispersion of ultrafine Pd nanoparticles within the HNTs’ lumen. A comprehensive analysis using CO-DRIFTS, TEM, H 2 -TPD, CO 2 -TPD, and Py-IR techniques revealed that the Pd/1.2M-HNTs catalyst possessed rich Pd step sites with a strong H 2 dissociation ability. Furthermore, the unique acid–base properties of the modified HNTs support moderate the adsorption strength of cyclohexanone, ensuring high selectivity by promoting its timely desorption and limiting over-hydrogenation. The optimized catalyst exhibited superior catalytic performance with a high turnover frequency (TOF) of 341 h −1 and excellent stability. This work highlights a facile and effective approach to control the support structure at the molecular level, offering new insights for the rational design of catalysts for hydrogenation reactions.