Finely control of product selectivity is an essential issue in organic chemical production. In the synthesis of functionalized anilines via reduction of the corresponding nitroarenes, the challenge is to selectively reduce only the nitro group in the presence of other reducible functional groups in nitroarene molecules at a high reaction rate. Normally, the nitroarene is reduced stepwise through a series of intermediates that remain as byproducts, increasing the aniline synthesis cost. Here we report that alloying small amounts of copper into gold nanoparticles can alter the reaction pathway of the catalytic reduction under visible-light irradiation at ambient temperature, allowing nitroaromatics to be transformed directly to anilines in a highly selective manner. The reasons for the high efficiency of the photocatalytic reduction under these comparatively benign conditions as well as the light-excited reaction mechanisms are discussed. This photocatalytic process avoids byproducts, exhibits a high reaction rate and excellent substituent tolerance, and can be used for the synthesis of many useful functionalized anilines under environmentally benign conditions. Switching of the reaction pathway simply by tailoring the bimetallic alloy NPs of the photocatalysts is effective for engineering of product chemoselectivity.
Abstract Titanate nanotubes (TNT) supported AgI nanoparticles were prepared by a two‐step method: the deposition of Ag 2 O on titanate nanotubes from AgNO 3 solution and the subsequent I‐adsorption process from NaI solution. It is found that the supported AgI samples exhibited excellent photoactivity for the selective oxidation of benzylamine to the corresponding imine under visible light illumination and the photocatalyst can be used for many times without apparent activity loss. X‐ray diffraction studies, transmission electron microscopy, diffuse reflectance UV‐Vis spectroscopy and nitrogen adsorption measurements were used for the characterization of the as‐prepared and recycled AgI samples. It is found that under visible light irradiation, AgI partially decomposed to produce Ag/AgI nanostructure and thus stabilized. The photoactivity of supported Ag/AgI for the selective oxidation of benzylamine was studied in terms of the light intensity, wavelength, temperature and substituent. It is proposed that the formation of plasmonic Ag nanoparticles should be responsible for the high activity and selectivity.
It is fascinating to explore the distribution of CO 2 hydrogenation products regulated by heterogeneous catalysts, as both the chemical state of surface metals and structure of the support itself of the supported catalysts may affect the performance of CO 2 hydrogenation. Here, the complete switching of CO 2 hydrogenation products from CH 4 to CO can be realized by induction of Cl into Ru/TiO 2 catalyst. DFT calculations indicated that Cl ions are mainly located on the Ru metal sites of Ru/TiO 2 catalysts, bader charge analysis and Ru 3 p XPS results suggested that electrons transferred from Ru to Cl, resulting in the decrease of electron density of Ru. In situ DRIFTS of CO 2 hydrogenation and CO adsorption proved that with the increase of the Cl ion content, the adsorption intensity of CO on the catalyst surface was significantly weakened, and resulted in the high CO selectivity. Our work demonstrates the positive role of Cl ions in regulating the distribution of CO 2 hydrogenation products, and provides new ideas for regulating other catalytic processes.
It is very difficult to selectively oxidise stable compounds such as toluene and xylenes to useful chemicals with molecular oxygen (O2) under moderate conditions. To achieve high conversion and less over-oxidised products, a new class of photocatalysts, metal hydroxide nanoparticles grafted with alcohols, is devised. They can efficiently oxidise alkyl aromatic compounds with O2 using visible or ultraviolet light or even sunlight to generate the corresponding aldehydes, alcohols and acids at ambient temperatures and give very little over-oxidation. For example toluene can be oxidised with a 23% conversion after a 48-hour exposure to sunlight with 85% of the product being benzaldehyde, and only a trace of CO2.The surface complexes grafted onto metal hydroxides can absorb light, generating free radicals on the surface, which then initiate aerobic oxidation of the stable alkyl aromatic molecules with high product selectivity. This mechanism is distinctly different from those of any known catalysts. The use of the new photocatalysts as a controlled means to generate surface radicals through light excitation allows us to drive the production of fine organic chemicals at ambient temperatures with sunlight. The process with the new photocatalysts is especially valuable for temperature-sensitive syntheses and a greener process than many conventional thermal reactions.
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