Thermally reduced gold nanocatalysts prepared by the carbonization of ordered mesoporous carbon as a heterogeneous catalyst for the selective reduction of aromatic nitro compounds

•Thermally reduced gold nanoparticles were prepared by carbonization of the matrix.•Particle morphology changed with neutral gold atoms in a low-coordination state.•Leaching- and aggregation-free gold was intercalated into spherical carbon.

In this study, we propose gold-intercalated ordered mesoporous carbon nanosphere catalysts in which gold nanoparticles are reduced by high-temperature carbonization of the carbonaceous matrix to catalyze the selective hydrogenation of aromatic nitro compounds. A spherical morphology of particles with size approximately 90 nm and ordered mesoporous arrays was clearly observed on the surface in the high-resolution scanning electron microscopy images. The X-ray photoelectron spectra and transmission electron microscopy images showed that the dispersed metallic gold nanoparticles (2.8 nm in diameter) were intercalated into a carbon framework. The IR spectra for CO chemisorption suggested the involvement of neutral gold atoms in a low-coordination state in clusters or a stepped surface. The gold nanocatalysts intercalated into the nanospherical mesoporous carbons exhibited high activity and selectivity for the hydrogenation of nitroarenes to the corresponding amines, using H2 as a reduction agent. The initial reaction rate reached 12.7 and 6.5 min−1 in the hydrogenation of p-chloronitrobenzene and 4-nitrophenol, respectively. This catalytic performance was retained for more than five catalytic runs with no obvious activity loss or gold leaching, indicative of high stability. The trapping test using a mercapto-functionalized SBA-15 solid revealed undetected soluble gold species in the reaction solution. The high activity and stability of the ordered mesoporous carbon nanosphere-supported gold catalysts was strongly correlated to the particle morphology change by thermal reduction, which can generate new low-coordinated gold atoms for intercalated gold NPs in the matrix.

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