Oxygen-doped carbon-supported palladium nanoparticles boost the tandem hydrogenation–acetalization–hydrogenolysis of phenols and diphenyl ethers to cyclohexyl ethers

Abstract

The one-pot hydrotreatment of phenols to cyclohexyl ethers is crucial but difficult to achieve for fine chemical synthesis owing to the easy overhydrogenation to cyclohexanols over traditional metal–acid bifunctional catalysts. Herein, surface oxygen-doped carbon-supported Pd nanoparticles (Pd/C-O) were prepared via nitric acid oxidation and subsequent incipient wetness impregnation, demonstrating the tandem hydrogenation–acetalization–hydrogenolysis route of phenol to cyclohexyl methyl ether, achieving an significant yield of 97.9% in a methanol solvent at a low temperature of 110 °C. Catalytic mechanism investigation indicated that the in situ hydrogen spillover from Pd nanoparticles to the Pd–O–C interface formed H⁺–H⁻ pairs, which acted as uncommon active sites for hydrogenation and hydrogenolysis steps and also provided Brønsted acid sites for the acetalization step, thereby triggering the facile preparation of cyclohexyl methyl ether. Furthermore, the prepared catalyst exhibited excellent catalytic generality for synthesizing cyclohexyl ethers from various phenols or alcohol solvents via a similar reaction route and great expansibility from diphenyl ethers via preliminary partial hydrogenation–alcoholysis steps. The study reports an interesting bifunctional catalysis for challenging tandem reaction routes toward cyclohexyl ether synthesis by harnessing an oxygen-doped carbon support to form transient H⁺–H⁻ pairs.