High efficient and stable thiol-modified dendritic mesoporous silica nanospheres supported gold catalysts for gas-phase selective oxidation of benzyl alcohol with ultra-long lifetime

Surface protective ligands play a pivotal role to dominate the physical and chemical performances of metal nanoparticles (NPs) at nanoscale interface. Herein, thiol-modified dendritic mesoporous silica nanospheres (DMSNs) supported Au NPs catalysts with tunable loading weight of thiol groups were prepared and used in gas-phase selective oxidation of benzyl alcohol with air as oxidant. The chemical reactivity and stability of the obtained Au NPs@DMSNs catalysts was strongly dependent on the loading weight of thiol groups grafted on the framework of DMSNs. Strikingly, the Au/DMSNs-4.4%SH catalyst with low loading weight of Au (∼2%) and thiol ligand (∼4.4%) achieved high conversion of benzyl alcohol (Conv. 91%) and selectivity for benzaldehyde (Sel. 98%) and unprecedented long lifetime up to 820 h at 250 °C, which surpassed all the reported Au based nanocatalysts. Through the study of the deactivation mechanism of Au NPs catalysts, the excellent catalytic performance and ultra-long lifetime of Au NPs catalyst was originated from the adsorption and packing of thiol groups on the surface of Au NPs, which limited the growth of Au NPs and concomitantly constructed a unique nanoconfined microenvironment at nanoscale interface for the synergistic adsorption and activation of reaction substrate and oxygen. Our results show the coverage-dependent ligand-induced surface effects on regulating the electronic structures, surface activity, optical properties, and chemisorption strength of metal NPs.