Oxygen Vacancy-Enriched\nAlumina Stabilized Pd Nanocatalysts\nfor Selective Hydrogenation of Phenols

The prevalence of electronic defects has not been successfully\ndemonstrated in nonreducible oxides. This work presents a straightforward\napproach to the preparation of a yellow alumina rich in F-centers\n(oxygen vacancies containing free electrons), which is well characterized\nby systematic spectral methods. The surface electron density of the\nas-prepared F-center enriched alumina sample was estimated to be approximately\n0.35 mmol·g<sup>–1</sup>. Free electrons on the surface\ncan reduce palladium precursors in situ, leading to the deposition\nof fine Pd nanoparticles on alumina. The produced Pd nanocatalysts\nare highly effective in the selective hydrogenation of phenol to cyclohexanone,\nachieving a high catalytic performance under mild conditions (30 °C\nand 0.1 MPa of H<sub>2</sub>). Systematic mechanism investigations\nreveal that hydroxyl radicals generated at the catalyst interfaces\nfacilitate the activation of phenol. The activated phenol is then\nsequentially hydrogenated to give the intermediate 2-cyclohexenone\nand then the desired cyclohexanone. The catalyst system demonstrates\nefficacy in selectively hydrogenating substituted phenols into a wide\narray of functional ketones.