| Heteroatom doped carbon materials have made remarkable achievements in the fields of catalytic oxidation,hydrogenation,electrocatalysis and energy storage devices.Among them,transition metal and nitrogen co-doped carbon nanocatalysts(M-N-C)have been widely used in liquid phase catalysis and electrochemistry because of its properties,including rich of raw materials,simple preparation method,high catalytic performance,stable chemical properties and so on.Therefore,it is very important to explore a green and sustainable method to prep are M-N-C catalyst with high catalytic performance.Biomass is widely distributed in nature as a renewable resource.Most of the biomass is rich in C and N elements,which is a natural precursor for the preparation of N-doped carbon nanomaterials.As a solvent and soft template,ionic liquids can effectively dissolve biomass and coordinate the pore structure of carbon materials.Metalloporphyrin,as macrocyclic metal organic compounds,consists of the structure of the transition metal atom M coordinated with four N atoms,which can provide a large number of MN_x active sites.The special structure can also limit the growth of metal particles under high temperature conditions and effectively promote the active sites disperse uniformly.In this paper,the M-N-C catalysts,prepared by double template methods with biomass and transition metal as precursors,are detected through a probe reaction and a series of characterizations for analysis and discussion.The main contents are:1)Ionic liquid(acted as soft template and solvent),casein(acted as carbon substrate),magnesium oxide(acted as a hard template)and cobalt porphyrin(acted as metal doped precursor)are dissolved in a pot and pyrolyzed at 500°C to obtained M-Co-N-C catalysts,and then a series of M-Co-N-C-X catalysts were etched in hydrochloric acid for different times.The experimental results show that the M-Co-N-C-9 catalyst has superior catalytic activity for the catalytic oxidation of ethylbenzene,and the ethylbenzene conversion is 96.5%and the selectivity of acetophenone is 99%.In addition,a series of characterization s show that the etching method can effectively remove magnesium oxide and large particles of cobalt particles,and promote the uniform dispersion of cobalt.At the same time,th e etching causes damage to the carbon layer to form more pore structures and increase the exposure of the active sites.Furthermore,the XPS result shows that the Co and N elements increase proportionally with the increase of etching time,which is consist ent with the change of catalyst performance,indicating that Co and N elements play an important role in promoting the catalytic performance of M-Co-NC-9.The catalyst active site may be CoN_x species.2)The pyrolysis of 1-butyl-3-methylimidazolium chloride,magnesium hydroxide,casein and cobalt porphyrins at different temperatures(600 ~?,700 ~?,800 ~?,900 ~? and 1000 ~?)is carried out to obtain black power,which was etched with hydrochloric acid and then a series of M-Co-N-C-9-T carbon nanocatalysts were prepared.The test results show that the pyrolysis temperature is closely related to the performance of the catalyst.Among them,M-Co-N-C-9-600 exhibits the optimum catalytic performance with ethylbenzene conversion is 98.1%and the selectivity of acetophenone is 99%.Analysis of BET and Raman spectra shows that the rise of temperature is benefitial to the increase of surface area.TEM and HRTEM analysis confirmed the presence of CoN_x species on the surface of M-Co-N-C-9-600.Further analysis of XPS shows that when the pyrolysis temperature is 600°C,the content of pyridinic N and Co atoms on the surface of the catalyst is the highest,indicating that the active site of the catalyst is CoN_x species.In addition,XPS can also find that not only the combination of pyridinic N and Co to form CoN_x promotes the conversion of ethylbenzene to acetophenone,but also the conversion of some N elements to graphite type N at high temperature plays an important role in promoting the performance of the catalyst.3)Calcining the mixture of 1-butyl-3-methylimidazolium chloride,magnesium hydroxide,casein and different amounts of cobalt porphyrin at 600°C,and the obtained black powder is uniformly etched for 9 h to prepare a range of M-Co_m-N-C-9-600 carbon nanocatalysts.By XPS and TEM analysis,the content of CoN_x active sites can be increased as the content of cobalt porphyrin increases,and evenly distributed on the carbon layer.The result of a series of characterization and cyclic experiments shows that the stability of M-Co_m-N-C-9-600 are improved with the increase of cobalt porphyrin doping amount,and the catalyst achieves the optimum cycle stability when m=0.1 g,when the loading is saturated. |
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