Selective hydrogenation of phenol to cyclohexanone over Pd nanoparticles encaged hollow mesoporous silica catalytic nanoreactors

Abstract

Pd nanoparticles (NPs) encaged hollow mesoporous silica nanoreactors (Pd@HMSNs) are prepared for hydrogenations of phenol, cresols and chlorophenols to cyclohexanone derivatives. Pd@HMSNs feature ∼ 4 nm Pd NPs in ∼ 16 nm hollow cavities of ∼ 30 nm HMSNs. Such Pd@HMSNs are highly thermally and catalytically stable. At mild reaction conditions, Pd@HMSNs efficiently catalyze hydrogenations of phenol and m-cresol to cyclohexanone derivatives with ≥ 98.3 % selectivity at ≥ 99.0 % conversions. Hydrogenations of o- and m-chlorophenol over Pd@HMSNs give cyclohexanone with ≥ 97.3 % selectivity at 100.0 % conversions, demonstrating a beneficial effect of such HMSNs for consecutive reactions. The confinement of Pd NPs inside hollow cavities of mesoporous nanoreactors greatly promotes collision times of reactant molecules with Pd NPs, resulting in an enhanced catalytic efficiency, while the residence of Pd NPs inside cavities provides a protecting effect for Pd NPs and is beneficial to thermal and catalytic stabilities.