The promoting role of minor amount of water in solvent-free hydrogenation of halogenated nitrobenzenes

This study shows that minor amount of water plays a very important role in solvent-free hydrogenation of halogenated nitrobenzenes. For dried sponge Pd, the reaction cannot occur in the absence of water. For Pd/C catalyst, minor amount of water reduces the induction time, increases the reaction rate and reaction TOFs. Water might enhance the diffusion, adsorption and dissociation of H2 on Pd catalysts.

Room-temperature hydrogenation of halogenated nitrobenzenes over metal-organic-framework-derived ultra-dispersed Ni stabilized by N-doped carbon nanoneedles

Ultra-dispersed Ni nanoparticles(7.5 nm)on nitrogen-doped carbon nanoneedles(Ni@NCNs)were prepared by simple pyrolysis of Ni-based metal–organic-framework for selective hydrogenation of halogenated nitrobenzenes to corresponding anilines.Two different crystallization methods(stirring and static)were compared and the optimal pyrolysis temperature was explored.Ni@NCNs were systematically characterized by wide analytical techniques.In the hydrogenation of p-chloronitrobenzene,Ni@NCNs-600(pyrolyzed at 600°C)exhibited extraordinarily high performance with 77.9 h^(–1)catalytic productivity and>99%p-chloroaniline selectivity at full p-chloronitrobenzene conversion under mild conditions(90°C,1.5 MPa H2),showing obvious superiority compared with reported Ni-based catalysts.Notably,the reaction smoothly proceeded at room temperature with full conversion and>99%selectivity.Moreover,Ni@NCNs-600 afforded good tolerance to various nitroarenes substituted by sensitive groups(halogen,nitrile,keto,carboxylic,etc.),and could be easily recycled by magnetic separation and reused for 5 times without deactivation.The adsorption tests showed that the preferential adsorption of–NO2 on the catalyst can restrain the dehalogenation of p-chloronitrobenzene,thus achieving high p-chloroaniline selectivity.While the high activity can be attributed to high Ni dispersion,special morphology,and rich pore structure of the catalyst.

High halogenated nitrobenzene hydrogenation selectivity over nano Ir particles

The selective hydrogenation of halogenated nitrobenzene over noble metal catalysts(Pd, Pt, and Ir) has attracted much attention owing to its high efficiency and environmental friendliness. However, the effect of size on the catalytic performance varies among different metal catalysts. In this study, sub-nano(<3 nm) Ir and Pd particles were prepared, and their catalytic properties for hydrogenation of halogenated nitrobenzene were evaluated.Results show that high selectivity(N 99%) was achieved over small Ir nanoparticles, in which the selectivity over the Pd with same size was much lower than that on Ir nanoparticles. Meanwhile, Ir and Pd have different hydrogen consumption rates and reaction rates. Density functional theory calculations showed that p-chloronitrobenzene(CNB) has different adsorption properties on Ir and Pd. The distance between oxygen(cholorine) and Ir is much shorter(longer) than that between oxygen and Pd. The reaction barriers of dechlorination of p-CNB and p-chloroaniline over different Ir models are much larger than those on Pd. Especially,lower coordination of Ir leads to larger barriers of dechlorination reaction. These theoretical results explain the difference between Ir and Pd on hydrogenation of halogenated nitrobenzene.

N-doped ordered mesoporous carbon as a multifunctional support of ultrafine Pt nanoparticles for hydrogenation of nitroarenes

Due to the advantages of high surface areas, large pore volumes and pore sizes, abundant nitrogen content that favored the metal-support interactions, N-doped ordered mesoporous carbons are regarded as a kind of fascinating and potential support for the synthesis of effective supported cat-alysts. Here, a N-doped ordered mesoporous carbon with a high N content （9.58 wt%）, high surface area （417 m^2/g）, and three-dimensional cubic structure was synthesized successfully and used as an effective support for immobilizing Pt nanoparticles （NPs）. The positive effects of nitrogen on the metal particle size enabled ultrasmall Pt NPs （about 1.0 ± 0.5 nm） to be obtained. Moreover, most of the Pt NPs are homogeneously dispersed in the mesoporous channels. However, using the ordered mesoporous carbon without nitrogen as support, the particles were larger （4.4 ± 1.7 nm） and many Pt NPs were distributed on the external surface, demonstrating the important role of the nitrogen species. The obtained N-doped ordered mesoporous material supported catalyst showed excellent catalytic activity （conversion 100%） and selectivity （〉99%） in the hydrogenation of halogenated nitrobenzenes under mild conditions. These values are much higher than those achieved using a commercial Pt/C catalyst （conversion 89% and selectivity 90%）. This outstanding catalytic perfor-mance can be attributed to the synergetic effects of the mesoporous structure, N-functionalized support, and stabilized ultrasmall Pt NPs. Moreover, such supported catalyst also showed excellent catalytic performance in the hydrogenation of other halogenated nitrobenzenes and nitroarenes. In addition, the stability of the multifunctional catalyst was excellent and it could be reused more than 10 times without significant losses of activity and selectivity. Our results conclusively show that a N-doped carbon support enable the formation of ultrafine metal NPs and improve the reaction ac-tivity and selectivity.