Nitrogen Doped Carbon Supported Iron,Cobalt Catalysts:Preparation And Their Application In Selective Reduction Of Nitrocompouds

Reduction of nitro-compounds widely used in the synthesis of dyes,pesticides,and medicines.The traditional protocols for reduction of nitrocompounds are catalytic hydrogenation and iron powder reduction.However,catalytic hydrogenation usually requires high pressure equipment;iron powder reduction generally causes serious environmental pollution,and will be prohibited in the future.Therefore,it is necessary to develop some alternative catalytic system for the selective reduction of nitrocompounds.Firstly,several catalysts Co NC-T composed of cobalt nanoparticles anchoring on nitrogen doped carbon were readily prepared through pyrolysis under nitrogen atmosphere of a multidentate-nitrogen ligand cobalt complex supported on biomass chitosan obtained via adsorption.These catalysts were tested in the reductive N-formylation of nitrocompounds with formic acid.It was found that the catalyst Co NC-700 obtained by pyrolysis at 700 ^oC showed best performance among the as-prepared catalysts.The influences of reaction conditions were investigated by using nitrobenzene as a model substrate,and the optimized reaction conditions were received,which were 10 equivalent formic acid,catalyst loading 1 mol%,reaction temperature 110^oC,reaction time 5 h,solvent acetonitrile.Under optimized reaction conditions the conversion of nitrobenzene reached 99%,and the selectivity towards N-phenylformamide reached 96.1%.This catalyst showed high activity and selectivity in reductive N-formylation of various nitroarenes and excellent chemoselectivity in the substrates with unsaturated functional groups.Characterization results revealed that most of the nitrogen atoms are present as graphitic N and pyridinic N,which act as anchoring sites of cobalt nanoparticles,and the cobalt nanoparticles are wrapped by nitrogen doped carbon layers preventing aggregation of nanoparticles,which endows the catalyst with excellent activity and superior reusability.Secondly,nitrogen doped carbon supported iron catalysts Fe NC-T were easily prepared through pyrolysis a mixed ligand iron complex supported on biomass chitosan as catalyst precursor under nitrogen atmosphere.The catalysts were applied to the selective reduction of 4,4'-dinitrostilbene-2,2'-disulfonic acid(DNS)to4,4'-diamino-2,2'-stilbenedisulfonic acid(DSD)with hydrazine hydrate as reductant,and Fe NC-800 performed best among as-prepared catalysts.The effects of reaction conditions on the reaction were screened and optimized reaction conditions were obtained,which were methanol:water of 2:3 as solvent,catalyst loading 50 mg,4.5 equiv hydrazine hydrate,reaction temperature 140 ^oC,and reaction time 5 h.Under the optimized conditions,the conversion of DNS reached 99%and the selectivity towards DSD reached83.1%.Characterization results reveal that iron species exist in the form of metallic iron and Fe₂O₃,and element C,N,Fe shows homogeneous distribution.The content of pyridinic N and graphitic N reached 63%in Fe NC-800 catalyst sample,which can serve as anchoring sites to stabilize iron nanoparticles.Larger surface area facilitates mass transfer and thereby endows Fe NC-800 catalyst with excellent performance.