Search

Regulating the surface properties of catalysts to control the selectivity of a reaction is a fascinating approach. Bulk polymeric carbon nitride exhibits a poor N-phenylhydroxylamine yield in nitrobenzene reduction reaction mainly due to the uncontrollable condensation side reactions. Thus, adjusting the structure of the catalyst was key to solving the above issue. Herein, –OH groups-modified polymeric carbon nitride was prepared via a simple hydrothermal treatment. With the introduced –OH groups replacing the terminal amino groups (–NH2) at the surface of the polymeric carbon nitride, a 3-fold increase in reaction rate was achieved, along with a high selectivity toward N-phenylhydroxylamine (ca. 80%). The introduced –OH group was found to be beneficial to the adsorption of the nitrobenzene, based on the density functional theory (DFT) calculation. It could also lower the recombination rate of photoinduced electron–hole pairs, which would accelerate the photocatalytic oxidation of isopropanol and supply more protons to participate in the hydrogen-transfer process. Moreover, the elevated conduction band position after –OH modification would provide high energetic photogenerated electrons to promote the reduction of nitrobenzene. These are all important to guarantee the highly selective production of N-phenylhydroxylamine. This paper not only provides a simple and green approach for the modification of polymeric carbon nitride toward an efficient photocatalyst, but also sheds light on the further study of the selective hydrogenation. [ABSTRACT FROM AUTHOR]

The successful hydrogenation of azobenzene on NaNbO 3 is inseparable with the trans -to- cis isomerisation under UV light irradiation. The moderate activation of N N bond in cis azobenzene on Nb site makes its hydrogenation reaction proceed smoothly. The 100 % selectivity towards hydrazobenzene over the surface of NaNbO 3 can be attributed to the weak interaction between NaNbO 3 and N N bond in hydrazobenzene. • The hydrogenation of azobenzene on NaNbO 3 was inseparable with azobenzene isomerisation under UV light irradiation. • The contribution from the cis -azobenzene isomer accounted for more than 70% in the hydrogenation process. • The weak interaction between NaNbO 3 and hydrazobenzene should be the root cause to avoid over reduction. NaNbO 3 fibre catalyst can efficiently hydrogenate azobenzene to hydrazobenzene with 100 % selectivity under Xe light irradiation. The catalytic activity was closely dependent on the trans - cis photoisomerisation of azobenzene and the subsequent moderate activation of cis N N bond on Nb site. The adsorption of azobenzene with cis or trans conformation on the Nb active site was investigated by the computational methods. The apparent increase of the cis N N bond length from 1.254 to 1.348 Å, suggested an effective activation. The important role of the cis isomer in the reaction was also reflected in the quenching experiment, in which a silver quencher was used to inhibit the generation of the cis isomer. The weak interaction between Nb site and N N of hydrazobenzene was the key to inhibit the over reduction, which was confirmed by the in situ diffuse-reflectance IR spectra. [ABSTRACT FROM AUTHOR]