Facilely Prepared Polymer-Derived Heteroatom-Doped Carbon-Based Catalysts For Metal-Free Catalysis

With the development of heterogeneous catalysis,it has become an important research target to build novel heterogeneous catalysts that are highly efficient,stable,environment-friendly and low cost.Traditional metal-based catalysts have always been dominant in heterogeneous catalysts due to their high catalytic activity.However,the high manufacturing cost,low structural stability and low environmental tolerance of traditional metal-based catalysts limit their further development and large-scale industrial application.Therefore,it is necessary to design a new type of catalyst with good catalytic stability and low cost.As novel heterogeneous catalysts developed in recent years,heteroatom-doped carbon-based metal-free catalysts have many advantages,such as abundant heteroatom-containing active sites,large specific surface area,porous structure,excellent structural stability and low manufacturing cost.More importantly,they can show metal-like catalytic activity.In various kinds of catalytic applications,the use of heteroatom-doped carbon-based metal-free catalysts can effectively reduce the manufacturing cost,improve the service life of the catalysts and prevent the secondary pollution caused by the loss of catalyst components on the basis of ensuring high catalytic activity,so they are ideal substitutes for the traditional metal-based heterogeneous catalysts.In this paper,a series of carbon-based metal-free heterogeneous catalysts were prepared by high temperature pyrolysis with various cost-efficient polymers as precursors and were successfully applied in catalytic processes of various important organic reactions.The main research contents are as follows:?1?A two-dimensional PC-COF containing abundant triazinyl and piperazinyl groups was constructed as a self-template and derived a series of N-doped carbon-based catalysts with high N contents?NC-X,X refers to the pyrolysis temperature?.The as-prepared NC-X catalysts contained abundant active sites resulting from N-doping and basically maintained the morphology and porous structure of PC-COF,and thus showed excellent catalytic activity and recyclability both in reduction of nitroarenes and Knoevenagel condensation of aromatic aldehyde derivatives.In addition,based on the experimental results and characterizations,the graphitic N in NC-X catalysts are the main catalytic active sites.?2?The P-doped porous carbon-based catalysts?PC-X,X refers to the pyrolysis temperature?with extremely high specific surface areas(>1600 m² g^-1)were prepared by simple physical mixing and high temperature carbonization process using soluble starch as carbon source and phosphoric acid as phosphorus source.This preparation method considerably reduced manufacturing cost and simplified preparation steps.As an efficient carbon-based catalyst,the PC-700 showed excellent catalytic activity and selectivity in aerobic selective oxidation of alcohols.Its catalytic activity is superior to other reported mono-heteroatom doped carbon materials and even comparable to the reported dual-heteroatom doped carbon materials.?3?A special polymer precursor composed of melamine-glyoxal resin and trithiocyanuric acid was constructed,in which melamine-glyoxal resin provided carbon skeleton and nitrogen source and trithiocyanuric acid provided sulfur source and abundant pore channels.The resulting N,S co-doped carbon-based catalysts?PDNSC-X,X refers to the pyrolysis temperature?with hierarchically porous structure and large specific surface areas were prepared by pyrolysis of the precursor.Due to the above structural advantages and the synergistic effect of N and S atoms doping,PDNSC-X showed excellent catalytic activity and selectivity both in reduction of nitroarenes and selective oxidation of ethylbenzene.In addition,the important roles of the doped S atoms and pyrrolic N atoms in catalytic activity and selectivity,respectively were discussed in detail.