Controlled Synthesis Of Ultrafine Metal Nanoparticles Confined In Porous Carbon And Their Catalytic Properties

Nitroarenes are regarded as the most common organic pollutants in industrial and agricultural wastewaters.The 4-nitrophenol（4-NP）,as one typical specie of nitroarenes,is difficult to dispose due to its high stability and solubility in water.Among the methods,the selective reduction of 4-NP to 4-aminophenol（4-AP）with NaBH₄ is of much interest,not only because this catalytic reaction is green and effective,but also the 4-AP is an important intermediate as reduction product that can be widely applied in dyestuffs and pharmaceuticals.Therefore,it is of great significance to develop environmentally friendly,highly activity and stability,remarkable catalytic activity catalysts for the reduction of nitroarenes.Bimetallic catalysts exhibit excellent catalytic activity and stability due to the synergistic effect between metals,and the size effect of metal nanoparticles is an important factor affecting the catalytic performance.With the development of nanoscience and technology,small-sized metal nanoparticle catalysts have gradually attracted widespread attention.For supported catalysts,the properties of the support have a certain influence on the catalytic performance.Porous carbon materials with high specific surface area,ordered pore structure and controllable pore size have been widely used in the catalytic field.This paper focuses on the catalytic performance of ultrafine bimetallic nanoparticles with synergistic catalytic effects in the hydrogenation of nitroarenes.The physicochemical properties of these catalysts were characterized by various characterization techniques.The effects of factors on the rate of hydrogenation reaction were investigated in detail.First,the ultrafine NiMoO_x NPs confined in mesoporous carbon with different morphology and composition by using replication method with SBA-15 as hard template.The ultrafine NiMoO_x NPs are uniformly dispersed without any aggregation and well-encapsulated into the mesopores.The pore structure of mesoporous carbon and the Ni/Mo composition valence-state are demonstrated as the main factors in the reduction of nitroarenes.NiMoO_x/mesoporous carbon-platelet（NiMoO_x/MC-PL）with short mesochannels and high surface area possesses excellent catalytic activity towards the reduction of 4-NP.The bifunctional mechanism or electronic synergistic effect between metal Ni and MoO_x species makes NiMoO_x/MC-PL-450 exhibit excellent catalytic activity,as well as the highest reaction rate constants k(0.650 min^-1)and TOF(0.242 s^-1).Secondly,a series of ultrafine PtRu nanoparticles embedded in porous carbon and molecular sieve were synthesized under microwave-assisted heating.The ultrafine PtRu nanoparticles are highly dispersed in the structure of molecular sieve and porous carbon materials and exhibit strong interaction between the supports.The composition/valence-state of PtRu,support and reaction parameters have an influence on the reduction rate of 4-NP.The bifunctional mechanism and/or electronic synergistic effects of Pt and Ru play an important role in the reduction of 4-NP with Pt/Ru mole ratio of 2.0.The Pt₂Ru supported on porous carbon exhibits the highest reaction rate constant k(0.894 min^-1)and TOF(0.317 s^-1)for4-nitrophenol（4-NP）reduction,and have an excellent reduction ability for other nitroarenes.In addition,a possible reaction mechanism for reduction of nitroaromatics was proposed.