Dual modification of TiNb2O7 with nitrogen dopants and oxygen vacancies for selective aerobic oxidation of benzylamine to imine under green light

TiNb2O7 powder was prepared by a simple hydrothermal method and subsequent heat treatment. Vo–N–TiNb2O7 was generated by NH3 and ethanol dual treatments. The NH3 treatment produced a new N 2p orbital band above the O 2p valence band and oxygen vacancy (Vo) levels were formed by the ethanol treatment. The photocatalytic performance of modified Vo–N–TiNb2O7 towards selective aerobic oxidation reactions under green light (475–600 nm, peaked at 525 nm) was measured. It exhibits a high conversion of benzylamine (above 90%) at 80 °C over 24 h with selectivity for N-benzylidenebenzylamine greater than 95% under green light, which is much better than the unmodified and mono-modified TiNb2O7. It is suggested that the dual modification alter the electronic band structure of TiNb2O7 and result in a narrower band gap which should be responsible for the enhanced photocatalytic activity

Reduction of nitrobenzene catalyzed by carbon Materials

The reduction of nitrobenzene catalyzed by different carbon materials (mainly carbon nanotubes) was studied. TGA, TPD, TEM, N-2 adsorption-desorption, and Raman spectroscopy were used to show that it was oxygenated groups that gave catalytic activity, while the surface area, pore structure, morphology, structural defects and Fe impurities in the catalysts did not have a significant influence on the activity. The carbonyl group played an important role, but the carboxylic group and anhydride adversely affected the reaction. The conjugated it system, which was necessary for electron transfer and nitrobenzene adsorption, was another critical factor. The reaction proceeded through the direct route in which the intermediate nitrosobenzene was converted directly to aniline quickly. (c) 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved

Hydroxyl-group-modified polymeric carbon nitride with the highly selective hydrogenation of nitrobenzene toN-phenylhydroxylamine under visible light

Regulating the surface properties of catalysts to control the selectivity of a reaction is a fascinating approach. Bulk polymeric carbon nitride exhibits a poorN-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 preparedviaa 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 towardN-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 ofN-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

Strong metal-support interaction induced O2 activation over Au/MNb2O6 (M = Zn2+, Ni2+ and Co2+) for efficient photocatalytic benzyl alcohol oxidative esterification

A series of metal niobates (MNb2O6, M = Zn2+, Ni2+ and Co2+) were prepared from H-niobate precursor under hydrothermal conditions, in which amino groups of L-lysine play an important role. Au nanoparticles were then supported on these niobates by NaBH4 reduction method. More importantly, the strong interaction between Au nanoparticles and ZnNb2O6 generates negatively charged Au which can activate molecular oxygen to form the exclusive high-active peroxide (NbOOAu) species on Au/ZnNb2O6 surface under visible light irradiation, observed in situ by diffuse reflectance infrared Fourier transform spectra (DRIFTS). The optimal NbOOAu species produced on the surface of Au/ZnNb2O6 can remove the H atom of the methylene group (−CH2–) of benzyl alcohol, leading to high photocatalytic activity of Au/ZnNb2O6 compared with Au/NiNb2O6 and Au/CoNb2O6. This modulation of interaction of Au and niobates for the activation of molecular oxygen provides a new prospect for highly selective photocatalytic oxidation reactions.</p

One-pot selective synthesis of azoxy compounds and imines via the photoredox reaction of nitroaromatic compounds and amines in water

A facile one-pot two-stage photochemical synthesis of aromatic azoxy compounds and imines has been developed by coupling the selective reduction of nitroaromatic compounds with the selective oxidation of amines in an aqueous solution. In the first stage (light illumination, Ar atmosphere), the light excited nitroaromatic molecule abstract H from amine to form ArNO2H and amine radical, which then form nitrosoaromatic, hydroxylamine and imine compounds. Water acts as a green solvent for the dispersion of the reactants and facilitates the formation of nitrosoaromatic and hydroxylamine intermediate compounds. In the second stage (no light, air atmosphere), the condensation of nitrosoaromatic and hydroxylamine compounds yields aromatic azoxy product with the aid of molecular oxygen in air. This photochemical synthesis achieved both high conversion and high product selectivity (>99%) at room temperature

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

NaNbO3 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[dbnd]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[dbnd]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.</p

Bidentate ligand modification strategy on supported Ni nanoparticles for photocatalytic selective hydrogenation of alkynes

The design of selective and stable non-precious metal catalysts for hydrogenation of alkyne is highly desirable. In this study, L-lysine modification strategy is applied to support Ni nanoparticles, which greatly improves the stability and photocatalytic performance in the hydrogenation of phenylacetylene to styrene. The robust stability is attributed to that both amino and carboxyl groups of L-lysine can function simultaneously as the anchor, much stronger than a single group, to strongly interact with metallic Ni via N and O coordination. The high selectivity to styrene is due to that L-lysine modification results in a larger adsorption energy difference between styrene and phenylacetylene on the surface of Ni, therefore phenylacetylene is preferentially adsorbed on Ni surface. This protocol shows that the modulation of interaction between ligands and Ni is favorable to design stable, active and selective catalysts for hydrogenation of alkynes

Probing the mechanism of benzaldehyde reduction to chiral hydrobenzoin on the CNT surface under near-UV light irradiation

Metal-free CNTs exhibit high activity (conversion rate 99.6%, 6 h) towards the synthesis of chiral hydrobenzoin from benzaldehyde under near-UV light irradiation (320–400 nm). The CNT structure before and after the reaction, the interaction between the molecule and the CNT surface, the intermediate products, the substitution effect and the influence of light on the reaction were examined using various techniques. A photo-excited conduction electron transfer (PECET) mechanism for the photocatalytic reduction using CNTs has been proposed. This finding provides a green photocatalytic route for the production of hydrobenzoin and highlights a potential photocatalytic application of CNTs