Design And Synthesis Of Heteroatoms Doped Carbon Based Catalysts For Catalytic Oxidation Of Hydrocarbons Research

In recent years,carbon-based materials,including zero-dimensional fullerenes,one-dimensional carbon nanotubes and three-dimensional graphite,have attracted much attention due to their desirable physical and chemical properties.These properties,including low cost,easy processing,diverse forms,relative chemical inertness,well-defined pores size and active sites for a series of redox reactions,make carbon-based materials not only have a good prospect in the field of electro?catalysis,but also be widely used in heterogeneous catalytic reactions.The carbon-based catalysts currently reported,which mainly depend on the choice of precursors and synthesis methods,are diverse.Therefore,selecting the appropriate precursor and developing a simple and efficient synthetic method are crucial for the preparation of highly efficient carbon-based catalysts.At present,the heteroatoms(such as N,B,P,S,and I atoms)doped carbon materials have attracted many researchers' attention because these doped heteroatoms are adjacent to the carbon atoms in the periodic table of elements,which can greatly change the surface structure and porous channel,enhance the hydrophilic,improve the electron transport rate and tune the compositions of materials,thus improving significantly the performance of materials.So far,researchers put their most of efforts on the design and synthesis of N doped carbon materials and develop other doped catalyst materials based on N doped strategy.Currently,the main method of heteroatoms doping is to directly dope heteroatoms during the synthesis of carbon materials,which is denoted as in-situ doping.The synthesized carbon based materials are treated by a precursor containing heteroatoms,which is denoted as post-treatment doping methods.In situ doping method is widely used because of its advantages such as simple method,less experimental steps and convenient control.This paper combines experiments with theories,a series of carbon-based materials preparation,characterization and application research are discussed systematically in this paper.It's mainly divided into the following parts:1),g-C3N4 is used as a carrier,and metal cobalt porphyrin is impregnated on g-C3N4 by impregnation method,and then after being pyrolyzed at the same temperature as the preparation of g-C3N4,a nitrogen-doped carbon-based catalyst(Co-N-Cx/g-C3N4)is obtained.In the metal porphyrin macrocyclic compounds,the molecular skeleton of nitrogen and metal are connected as metal nitrogen bonds.This bond bridge connects the metal particles evenly to the catalyst.There is no apparent aggregation of metal particles in the TEM/HRTEM images,which confirms this opinion.Co-N-C and g-C3N4 have a low conversion rate(<15%)for solvent free oxygen oxidation of ethylbenzene,while the conversion rate of Co-N-C0.2/g-C3N4 with the optimum loading amount reaches 28%.Through the detailed characterization and analysis of the catalyst,the good catalytic activity comes from the active center Co-Nx,and the synergistic effect between and Co-N-C and g-C3N4?2),Melamine is using as carbon and nitrogen source,citric acid is using as chelating agent while chelating metal particles and protonated melamine,and then the system is slowly heating up to 800 ? to form N-doped carbon nanotubes with coated metal particles(Co@GCNs).The catalyst exhibits high conversion and selectivity for solvent free oxygen oxidation of ethylbenzene(68%and 93%respectively).Through the detailed characterization analysis of the catalyst and a series of controlled experiments,this special structure can not only make full use of the advantages of N doped carbon nanotubes,but also make use of the characteristics of high activity of metal particles.The catalytic activity can be further improved by triggering synergistic effect between them.3),S-CoNC is obtained via a high temperature heating,in which KSCN is used as S sources,and KSCN can be the pore forming agent,and phenanthroline is using as carbon,nitrogen resources;the obtained S-doped materials have high specific surface area and porous structures.The specific surface area of the catalyst is 183 m2/g,which is much larger than the specific surface area of the composite catalysts from phenanthroline precursor(CoNC/CNT and CoNC/CB)loaded on the carbon nanotubes or carbon black,and the catalyst contains a large amount of Co4S3 through XRD and HRTEM analysis.When the reaction is extended to 20 h,the catalyst has a very high catalytic activity and the conversion rate can reach over 80%.After a detailed comparison test and analysis of the composition of the catalyst,it is found that the catalyst exhibits high catalytic energy and the S-CoNC has a high ratio of defects when the presence of Co4S3.Therefore,combined with high defects and Co4S3,S-CoNC has excellent catalytic activity.The methods of three kinds catalysts are simple,green,no surfactant and nontoxic organic solvents,and the high content of nitrogen is even can be controlled by changing the number of precursor.The the green catalytic reaction of ethylbenzene oxidation reaction was used as a probe reaction to explore the performance of the catalysts in the absence of solvents,oxygen as oxidants,we finally achieved the gradually increase of conversion rate and selectivity.From about 20%of conversion and 77%of selectivity of the first catalyst to about 70%and 93%of the second catalyst,respectively,and finally up to 80%and 90%,we achieved a breakthrough in the efficiency of catalytic oxidation in the green reaction process.