Study On The Design And Construction Of Catalysts For The Liquid-Phase Hydrogenation Of 4-Nitrophenol And Their Catalytic Performances

Among the various kinds of refractory organic pollutants,the treatment of nitroaromatic compounds represented by 4-Nitrophenol(4-NP)has attracted great attention.4-NP is difficult to be degraded naturally,and easy to be enriched in organisms or human,which has potential toxic effects of mutagenesis,carcinogenesis and teratogenesis on human body.The catalytic hydrogenation of 4-NP is favorable due to the advantages that the negative effluence of 4-NP on the environment can be eliminated and also 4-Aminophenol(4-AP)as a value-added organic intermediate can be generated through hydrogenation.4-AP has a large global demand,which can be intensively applied in the pharmaceutical,pesticide,rubber and dye industries.The challenge in this field is the design and development of new efficient catalysts,which has important theoretical and practical significance.In terms of the highly effective liquid-phase hydrogenation of 4-NP,three types of catalysts were designed including supported,coated and heteroatom-doped carbon catalysts,which covers precious metal catalysts,non-noble metal catalysts and metal catalysts.In addition,the relationships between the catalyst composition,structure,morphology,surface/interface control,etc.and the catalytic performances were thoroughly investigated.Finally,the possible reaction pathway was proposed.The specific contents are as follows:1.Synthesis,characterization and catalytic study of 4-NP liquid-phase hydrogenation with supported highly dispersed Ag-based catalystsThe porous Co3O4 nanosheets(COS)synthesized by a simple hydrothermal method were employed as the support,and then Ag nanoparticles(NPs)were loaded on the COS by NaBH4 liquid-phase reduction to prepare a highly dispersed Ag based catalyst(ACOS).The ACOS catalysts were characterized by XRD,SEM,TEM,HRTEM,XPS,N2 adsorption-desorption,etc.The results showed that Ag NPs(with an average size of 9.5 nm)were evenly dispersed on the COS surface.The catalyst has a mesoporous structure,and the surface area of the ACOS is calculated to be 24.6 m2 g-1.The synthesized ACOS was applied for the reduction of 4-NP liquid-phase hydrogenation reaction.The excellent catalytic performance of the ACOS(Kapp was 0.122 min-1,and TOF was 2.4 mmol g-1 h-1)can be mainly attributed to the uniformly anchored Ag NPs,the porous structure with high surface area and the synergistic effect between Ag NPs and Co3O4 support.These advantages provided abundant and stable active sites and rapid interfacial electron transfer for 4-NP hydrogenation,thus improving the catalytic performance.In addition,the recycling performance tests showed that no obvious decrease in the catalytic activity can be found after five successive cycles.In addition,it was found that 4-NP and BH4-had competitive adsorption on the surface of the ACOS catalyst by investigating the catalytic behavior at different reaction temperatures and reactant concentrations.These results demonstrate that the 4-NP reduction reaction catalyzed by the ACOS follows L-H model.Furthermore,a plausible catalytic mechanism was proposed.2.Construction of nanometer needle self-assembled flower-like Co@NC-MF catalyst and its application in 4-NP liquid-phase hydrogenationIn this chapter,a flower-like Co@NC-MF catalyst self-assembled by nanoneedles was synthesized by one-step hydrothermal and post-calcination treatment.The series of Co@NC catalysts were characterized through XRD,SEM,TEM,HRTEM,TG,XPS,N2 adsorption-desorption techniques.The Co@NC-MF catalyst with the best catalytic performance possessed a unique structure of self-assembled flower-like nanoneedles,and the internal Co NPs(average particle size 20.1 nm)were successfully embedded in the nitrogen-doped carbon layer.The Co@NC-MF catalyst was applied in the liquid-phase hydrogenation reaction of 4-NP,which presented excellent catalytic performance(Kapp was 0.228 min-1,and TOF was 3.3 mmol g-1 h-1).Additionally,the catalyst can be magnetically separated,and the recycling performance test showed that the activity of the catalyst did not decrease obviously after 5 cycles.The investigations of the influence of the synthesis conditions on the catalytic performance indicated that the content of cobalt source,the addition of urea and the calcination temperature had greater influences on the morphology,size and catalytic performance of the Co@NC catalysts.Besides,the studies regarding the impact of oxidation and acid-washing treatments on the catalytic performances suggested that the excellent performance of Co@NC-MF catalyst can be attributed to the uniform and stable Co NPs and the interfacial synergistic effect between the N-doped carbon layer and Co NPs.3.Green controllable preparation of N-doped porous carbon catalyst derived from radish and its application in 4-NP liquid-phase hydrogenationIn this chapter,dry radish powder was used as the carbon source,urea as the external nitrogen source,and KOH as the activator.N-doped porous carbon catalysts(NKC series)were prepared by calcining the mixed reactants in N2 atmosphere.A series of synthesized NKC catalysts were studied through XRD,SEM,TEM,Raman,TG,XPS and N2 adsorption-desorption characterizations.The synthesized NKC series catalysts were applied in the liquid-phase hydrogenation reduction of 4-NP.Among the series of catalysts,the NKC-3-800 with the highest catalytic activity presented a specific surface area of 2163.3 m2 g-1,a pore volume of 1.88 cm3 g-1,and an N doping amount of 11.8 at.%.The reaction results indicated that the hydrogenation performances of the NKC catalysts were not influenced by the total amount of N doping but were closely related to the content of graphite nitrogen.Among them,the NKC-3-800 had the best catalytic performance(Kapp was 0.275 min-1,and TOF was 10 mmol g-1 h-1),which is comparable to or even better than the reported metal or even precious metal catalysts.In addition,4-NP and BH4-also had competitive adsorption on the surface of NKC-3-800 catalyst by performing the reactions at different reaction temperatures and reactant concentrations,and the catalytic reaction behavior was in line with the L-H model.This provides more feasibility for the efficient application of cheap and easily available biomass in the field of 4-NP catalytic hydrogenation,which should possess a good application value and a bright future.