The key role of photoisomerisation for the highly selective photocatalytic hydrogenation of azobenzene to hydrazobenzene over NaNbO3 fibre photocatalyst.

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]