Abstract
The effect of the divalent metal ions on the hydrotalcite (HT) (MAl-HT; M = Mg, Zn, Ni)-supported thiolated Au25 nanoclusters (NCs) as the precatalysts for the chemoselective hydrogenation of 3-nitrostyrene to 3-vinylaniline was investigated. The highest chemoselectivity was obtained over the Au25/ZnAl-HT-300 (calcined at 300 °C) catalyst, with a maintained selectivity of desired product above 98%. The Au25/NiAl-HT-300 catalyst exhibited the highest activity, although the particle size of gold (3.2 nm) was greater than those of the Au25/MgAl-HT-300 (2.2 nm) and Au25/ZnAl-HT-300 (1.7 nm) catalysts. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results of CO adsorption revealed that Ni interacting intimately with gold could be reduced easily, which affected the catalytic behavior of the Au25/NiAl-HT-300 catalyst. Furthermore, the results of the in situ DRIFTS of the adsorption of nitrostyrene at 10 bar of hydrogen suggested that, besides the condensation route, it also followed the direct route to produce aniline on Au25/NiAl-HT-300, which was different from the other two catalysts. This work provides new insight into the support effect over the gold catalysts for selective hydrogenation reactions.
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