Nanospherical mesoporous carbon-supported gold as an efficient heterogeneous catalyst in the elimination of mass transport limitations

摘要

This study proposes ordered mesoporous carbon nanosphere-supported gold catalysts to eliminate the diffusion limitation inside the long channels of bulk mesoporous materials. The nanospherical catalysts have a spherical morphology with a diameter of approximately 90 nm, uniform pore sizes of 2.5 nm, and high surface areas of approximately 600 m(2)/g; and the bulk catalysts have similar mesoporous textural properties with nanospherical catalysts but an irregular bulk shape. Metallic gold particles are both intercalated inside carbonaceous walls. The Madon-Boudart (MB) test shows that nanospherical catalysts exhibit no diffusion limitations in the reduction of nitroarenes, even for a large 2,6-dimethylnitrobenzene (2,6-DMNB) molecule. By comparison, the bulk-ordered mesoporous carbon-supported gold catalysts display distinct mass transfer inhibition. The nanospherical mesoporous carbon-supported gold catalysts are highly active and selective for the reduction of nitroarenes to corresponding amines, reaching turnover frequency (TOF) values of 13.7, 16.1, 7.6 and 26.8 min(-1) for converting 4-nitrophenol (4-NP), 2-nitrophenol (2-NP), 4-(tert-butyl)-2-nitrophenol (4-TB-2-NP), and 2,6-DMNB, respectively. The catalysts are stable and can be re-used more than 15 times.