| Catalytic hydrogenation of nitrobenzene to aniline is the most suitable green process for industrial production of aniline.Aniline has great market potential and competitiveness due to its wide application and technological innovation.With the rapid development of petrochemical industry,the output of phenol is increasing with each passing day.The efficient utilization of phenol has become a research hotspot in the field of chemical industry.Pdis one of the excellent catalysts in hydrogenation.In addition,the confined Pdcatalyst can make Pdevenly disperse in the support and improve the utilization of metal atoms.The hyperbranched polymers have a large number of terminal hydroxyl groups and unique internal cavities,which can fix and disperse metal particles and improve the activity and stability of the catalyst.At the same time,the simple preparation process and low cost make it suitable for large-scale production.Therefore,in this paper,a new kind of confined Pdnanocatalyst(Pd@H102-350)as well as confined bimetallic Pd-Iralloy nanocatalyst(Pd-Ir@H102-350)with using hydroxyl-terminated hyperbranched polymer(H102)as a support.Combined with the self-assembly of H102,the structures of the as-synthesized catalysts were analyzed and characterized,and their catalytic performances in hydrogenation were also investigated.Pdnanomaterials loaded with H102 self-assembly(Pd@H102)were prepared by oil bath reduction at 100 ℃ for 1 h by using PdCl2 as the precursor,H102 as the carrier,isopropanol as the solvent in the presence of an appropriate amount of NaHCO3.And then A novel Pdnanocatalyst confined within the partially carbonized self assembly of hyperbranched polymer was successfully prepared(Pd@H102-350)with Pd@H102 calcined at 350 ℃ for 2 h in nitrogen atmosphere.In the reaction system,the molar ratio of PdCl2/H102/NaHCO3 was 1/2/3,in which the volume of isopropanol was 20 ml and the amount of PdCl2 was 0.5 mmol.The effects of reaction parameters such as solvent,reaction temperature,reaction time and the amount of additive on the preparation of the catalyst were systematically investigated.The as-synthesized catalyst,Pd@H102-350,was characterized by TEM,STEM,SEM,XRD,XPS,FT-IR and TG.The as-synthesized Pd@H102-350 composite nanonaterials showed spherical cavity structures.Pdnanoparticles with an average size of 4.25 nm were distributed within the cavity walls of the partially carbonized self-assembly structure of hyperbranched polymer.The controlled synthesis mechanism of composite nanocatalytic materials Pd@H102-350 was clarified preliminarily.The hydrogenation of nitrobenzene and its derivatives over composite nanocatalyst Pd@H102-350 at room temperature was studied.The effects of solvent,reaction time and hydrogen pressure on the catalytic performance of Pd@H102-350 catalyst were investigated.The results showed that 100% conversion of nitrobenzene and >99.9% aniline selectivity were achieved over Pd@H102-350 catalyst with ethanol as a solvent at room temperature for30 min under a H2 pressure of 0.5 MPa.After ten cycles,the Pd@H102-350 catalyst maintained over 99% conversion and aniline selectivity,suggesting a high reusability and stability besides excellent activity.Under the same conditions,Pd@H102-350 demonstrated the same high conversion and selectivity for the catalytical hydrogenation of nitrobenzene and its derivatives.The mechanism of nitrobenzene hydrogenation over the catalyst was investigated.The composite nanocatalyst Pd@H102-350 also showed high catalytic activity in the selective hydrogenation of phenol to cyclohexanone.The conversion of phenol and the selectivity of cyclohexanone were 99.8% and 87.9%,respectively,in water at 85 ℃ for 4 h under 0.75 MPa H2 pressure.As a result,The composite catalyst Pd@H102-350 can be used not only for the rapid and efficient selective hydrogenation of nitrobenzene and its derivatives at room temperature and low hydrogen pressure,but also for the highly selective hydrogenation of phenol to cyclohexanone.Pd-Iralloy nanomaterials loaded with H102 self-assembly(Pd-Ir@H102)were prepared by oil bath reduction at 120 ℃ for 1 h by using PdCl2 and IrCl3 as the precursors,H102 as the carrier,isopropanol as the solvent in the presence of an appropriate amount of NaHCO3.And then A novel Pd-Iralloy nanocatalyst confined within the partially carbonized self assembly of hyperbranched polymer was successfully prepared(Pd-Ir@H102-350)with Pd-Ir@H102calcined at 350 ℃ for 2 h in nitrogen atmosphere.In the reaction system,the molar ratio of(PdCl2+IrCl3)/H102/NaHCO3 was 1/2/2.5,in which the volume of isopropanol was 20 ml and the amount of PdCl2 and IrCl3 was 0.25 mmol,respectively.The as-synthesized catalyst,Pd-Ir@H102-350,was characterized by TEM,STEM,SEM,XRD,XPS and FT-IR.The results showed that as-synthesized Pd-Ir@H102-350 also shows the similar spherical cavity structure characteristics to the catalyst Pd@H102-350.Pd-Iralloy nanoparticles with an average size of 1.93 nm were dispersed within the cavity walls of the partially carbonized self-assembly structure of hyperbranched polymer.The composite nanocatalyst Pd-Ir@H102-350 demonstrated excellent catalytic performance in the selective hydrogenation of nitrobenzene and its derivatives to aromatic amines.The results showed that 100% conversions of nitrobenzene and its derivatives and >99.9% selectivities of the coresponding aromatic amines were achieved over Pd-Ir@H102-350 catalyst with ethanol as a solvent at room temperature for 45 min under a H2 pressure of 1 MPa.And the catalytic activity maintained unchanged after ten cycles,suggesting a high reusability and stability. |
