Preparation Of Copper Based Carbon Material Catalysts And Their Catalytic Performance For Phenol Degradation

Cu-based catalysts show high activity in the oxidation process and are widely used to study the catalytic wet air oxidation(CWAO)of refractory organic wastewater.Among the common catalyst supports,activated carbon is extensively employed to load active metals in the CWAO field due to its high specific surface area,rich pore structure,diverse surface groups,and excellent adsorption performance.With Cu as the active component and activated carbon as the support,Cu-based carbon material catalysts are considered to be excellent catalysts.Although extensive research has been carried out,the catalysts still have the following problems:(1)The active component Cu tends to agglomerate on the surface of the support during the preparation process,and the dispersion of Cu is poor;(2)Cu is easily leached during the CWAO reaction process;(3)The structure-activity relationship between the catalytic performance and the Cu and N components of Cu-based nitrogen-doped carbon material catalysts prepared by one-step nitrogen doping and loading active metals is not clear.Therefore,it is imminent to develop a series of Cu-based carbon material catalysts with high catalytic activity,high stability,and low cost to solve the drawbacks of Cu-based catalysts.Thence,in this paper,a series of Cu-based carbon materials(Cu/AC)catalysts were prepared by precursor impregnation method(PI)with walnut shells as carbon material precursor and copper-ammonia solution as copper source.The effects of preparation method,impregnation ratio,carbonization and activation conditions on the pore structure characteristics,surface valence state distribution of Cu,the dispersion of Cu et al.characteristics of Cu/AC catalysts and their catalytic performance were studied comprehensively.Based on the above research,to further improve the catalytic performance of Cu/AC,the doping of promoter Ce and the method of one-step doping with nitrogen and loading of active metal were used.The characteristics of the modified Cu-based carbon material catalyst and the impact of the modification on their catalytic performance were also studied.The main conclusions are as follows:1.Compared with the activated carbon impregnation(ACI)methods,the precursor impregnation method(PI)had the following advantages:[Cu(NH3)4]2+was adsorbed and complexed with acetamido,Carboxyl and other polar functional groups in the pores and surface of biomass during the preparation of the catalyst,which enabled Cu to be embedded in the carbon framework of the carbon material support,thereby the catalyst achieved a Cu content of up to 1.77%.The relationship between the impregnation ratio and the Cu content was y=0.3571x,R2=0.9989.Due to the catalytic effect of Cu during the carbonization and activation process,the micropore volume of catalyst increased by 7%,and the specific surface area increased.In the PI catalysts,Cu species coexisted of Cu2+and(Cu++Cu0),and CuO had a microcrystalline structure.The PI method improved the dispersion of Cu species,resulting in the more evenly distribution of CuO and Cu2O on the surface of catalysts.The catalysts prepared by the PI method had higher ratio of(Cu++CuO)/Cu2+and lattice oxygen content,which helped to improve the catalytic activity.2.The PI catalyst with the impregnation rate of 3(PI-3)exhibited the best catalytic activity during the phenol oxidation process.When the reaction proceeded for 8.5 h,the conversion rates of phenol and COD reached 95.1%and 85.2%,respectively.The precursor impregnation method could effectively suppress the loss of Cu component in the catalyst.While the average Cu ion leaching concentration of the treated solution was only 1.18 mg/L.3.The catalytic performance of Cu/AC catalysts was closely related to Cu+species in Cu/AC catalysts.During the reactions,the redox cycle of Cu+/Cu2+generated O2-·,HO2·,and H2O2,while H2O2 contributed to the generation of HO· and other free radicals.Higher Cu+ content could accelerate the redox transformation of Cu+/Cu2+,promote the generation of free radicals,and thus improve the conversion rate of phenol and COD.HO· and O2-··had a significantly promoting influence on the degradation of phenol and COD during the CWAO reaction,of which HO· played the dominant role.4.The impact of the carbonization conditions on the characteristics of Cu/AC catalysts is clarified.When the carbonization temperature increased in the range of 500?800?,the specific surface area and pore volume of Cu/AC increased slightly,but more volatiles generated during the carbonization process,which promoted the reduction of Cu2+to Cu+and Cu0.In turn,the content of(Cu++Cu0)on the surface of catalysts increased.All these gave rise to the catalytic activity of Cu/AC gradually increased as the carbonization temperature increasing.When the carbonization time extended in the range of 1?4 h,the content of(Cu++Cu0)decreased,and Cu2O and CuO were better incorporated into the carbon material support thus increased the lattice oxygen content.The catalytic activity of Cu/AC showed a trend of increasing first and then decreasing slightly with the prolongation of carbonization time.5.With the activation temperature increased in the range of 800?920? and the activation time extended in the range of 1?3 h,a large number of micropore formed in Cu/AC,and the specific surface area and micropore volume of Cu/AC increased from 544.5 m2/g and 0.2500 cm3/g to 1096.1 m2/g and 0.5073 cm3/g,respectively,which improved the adsorption performance of Cu/AC to phenol and other organic substances.The increase of activation temperature and the extension of activation time contributed to the decomposition of a large number of oxygen-containing functional groups in Cu/AC,which oxidized the Cu+ and Cu0 produced during the carbonization process to Cu2+ again,resulting in the content of(Cu++Cu0)decreased,while the lattice oxygen content increased.With the interaction of specific surface area,surface(Cu++Cu0)and lattice oxygen of Cu/AC catalysts,the catalytic activity of Cu/AC gradually increased with the increase of activation temperature,and increased firstly and then decreased slightly with the extension of activation time.6.The optimal carbonization and activation conditions for Cu/AC were carbonization temperature 800?,carbonization time 2 h,activation temperature 880?,activation time 2 h.The resulting Cu/AC catalyst exhibed good stability as well as low Cu ion leaching concentration and achieved 99.0%conversion of phenol and 90.6%conversion of COD within 8.5 h of reaction.7.The introduction method of the promoter Ce had a significant influence on the catalytic properties of Ce-modified Cu-based carbon material(CeCu/AC)catalysts.For the catalysts introduced of Ce by activated carbon impregnation(ACI)method,3Ce3Cu/AC-I,metal oxide particles were formed and blocked the channel of the catalyst during the calcination process,resulting in a reduction in the micropores genernated and a decrease in the specific surface area.At the same time,the Cu content of the 3Ce3Cu/AC-I catalyst decreased.And the reunion phenomena of Cu on the surface of catalyst was still obvious.Compared with the unmodified catalyst,the catalytic activity of the 3Ce3Cu/AC-I catalyst was significantly reduced.The introduction of Ce by precursor impregnation(PI)method could significantly promote the formation of micropore,thus the specific surface area of the catalyst reached 653.0 m2/g and the micropore volume increased by 30.2%.After the modification,the content of Cu and Ce in the catalyst greatly increased.Meanwhile,the interaction between Cu and Ce on the surface of the 3Ce3Cu/AC-? catalyst as well as the interaction between active metal and carbon material support remarkly enhanced,improving the dispersion of Cu species on the surface of the catalyst.The introduction of Ce by PI method significantly increased the Cu+ content and the chemically adsorbed oxygen content on the surface of 3Ce3Cu/AC-?,which accelerated the generation of free radicals during the reaction,thereby greatly enhanced the catalytic activity and stability of the catalyst.At the same time,the introduction of Ce by PI method effectively suppressed the loss of Cu species and inhibited the carbon deposition during the reaction.8.In the preparation process of Ce-modified catalyst prepared by PI method,Ce loading also had a significant effect on the catalyst performance.The increase of the Ce loading could promote the formation of micropores in the catalyst,and the specific surface area of the catalyst increased accordingly.Meanwhile,the relative content of Cu+ and Ce3+ on the catalyst surface increased.The synergistic effect between Ce and Cu promoted the occurrence of ions conversion between Ce4+(?)Ce3+ and Cu2+(?)Cu+,which improved the catalyst's redox capacity.The catalyst with Ce loading of 3%exhibited the best catalytic activity and stability.After reacted for 5 h,the conversion rates of phenol and COD maintained as high as 99.5%and 95.7%respectively.9.The nitrogen species and active metal Cu were simultaneously introduced into the catalyst surface effectively by one-step doping of nitrogen and loading of active metal method.After the modification,the nitrogen content in the Cu-based N-doped catalyst increased markedly,and nitrogen-containing functional groups such as pyridine nitrogen and pyrrole nitrogen formed.The introduced Cu species were evenly distributed on the surface of the catalyst surface in the form of coexistence of Cu,Cu2O,and CuO.10.During the preparation of Cu/HTC-N catalyst,the solid-liquid ratio and other factors had significant effects on the pore structure characteristics of the catalyst as well as the content and distribution of Cu,N,and O elements on the surface of the catalyst.The increase of the solid-liquid ratio was helpful to the formation of micropores and the increase of the specific surface area of the catalyst.The content of Cu+ and nitrogen on the catalyst surface increased at the same time,which contributed to enhancing the catalytic activity of the catalyst.When the Cu loading increased,the introduction of excessive Cu led to a decrease in the specific surface area and the degree of graphitization of the catalyst.However,the content of Cu,N,and O on the surface of the catalyst increased persistently,and the catalytic activity of the catalyst showed a trend of increasing first and then decreasing.With the increase of the hydrothermal temperature,the specific surface area of the catalyst continued to increase,and the contents of Cu+,pyridine nitrogen and pyrrole nitrogen all increased dramatically,which improved the catalytic activity and stability.With the extension of the hydrothermal time,the content of N on the catalyst surface increased by about 40%,and the content of pyridine nitrogen and pyrrole nitrogen was as high as 42.4%.The optimal preparation conditions of Cu/HTC-N catalyst were solid-liquid ratio 1:20,Cu loading 5%,hydrothermal temperature 200?,hydrothermal time 16 h,and the resulting catalyst reached 99.3%conversion of phenol and 96.2%conversion of COD within 5 h of reaction.