Preparation Of Co-N-C Catalyst And Its Catalytic Properties For The Oxidation Of Aromatic Hydrocarbons To Corresponding Oxygenated Compounds

Transition metal-coordinated nitrogen doped carbon materials have been widely used in the field of electrocatalysis and liquid catalysis due to their cheapness,chemical stability and so on.At present,many kinds of M-N-C catalysts have been developed,but they mainly depend on the selection of precursors and synthetic methods.Therefore,it is very important to select a suitable precursor and develop a simple and effective synthesis method for the preparation of highly efficient M-N-C catalysts.Metalloporphyrin,as a metal macrocyclic compound,consists of alternating chains of N-containing ligands and metal ions.The existence of a robust ligand bridge between metal ions efficiently promotes the dispersion of metal particles in the catalyst.However,the direct calcination of metalloporphyrin precursors generates catalysts with small surface areas,and the activity and stability of the catalysts need to be further improved.It is possible to improve the catalytic activity and stability by impregnation method,but the preparation process is complicated,and the morphology and structure of the catalyst depend on the structural properties of the carrier.In a recent study,ionic liquid based approaches are reasonable,simple and effective ways to synthesize N-doped carbon materials.Ionic liquids can not only be used as solvent,pore forming agent and structure directing agent,but also can be used as dopant to synthesize various doped porous carbon materials.In this paper,the preparation of M-N-C from above several aspects and the research contents are as follows:1.The Co-N/C catalyst has been synthesized by impregnating cobalt porphyrin complex on commercially available carbon black and subsequent pyrolysis at high temperature.Liquid phase oxidation of ethylbenzene as a probe reaction using TBHP as oxidant,the optimum reaction conditions were screened out and the activation energy(Ea)for the catalytic oxidation of ethylbenzene was calculated.The experimental results show that Co-N/C-700 has the highest catalytic activity(ethylbenzene conversion is 97%,the selectivity of acetophenone is 99%)and stability,which is attributed to the high graphite nitrogen and Co-N(the sum is 53.9%)of catalysts,coupled with crucial synergistic effect between the Co-O,Co-N and N-C moieties.In addition,activation of the catalytic oxidation of ethylbenzene is 22.2 ± 2.1 kJ mol-1 and the catalytic system features a broad substrate scope for various saturated C-H bonds.2.The Co-N-C catalyst has been prepared by a simple and economical soft template stategy.With 1-butyl-3-methylimidazolium bromide as soft template and pore forming agent,and then directly carbonization of cobalt porphyrin and ionic liquid system.Compared with the direct pyrolysis cobalt porphyrin,the metal particles are relatively small(1.5?3.5 nm)and the specific surface area is relatively large(10?30 m2·g-1).The catalytic activity of the catalyst has been investigated with oxygen as oxidant and solvent-free condition.A series of comparative experimental results show that the catalyst has good catalytic activity and stability than that of the catalysts prepared by traditional impregnation method and metal supported catalyst.3.A nitrogen and boron codoped and highly crystalline metal porous carbon material has been synthesized through cothermal condensation of the 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and cobalt porphyrin.In this approach,the ionic liquid acted as both a soft template and a heteroatom precursor,cobalt porphyrin acted as metal,nitrogen and carbon sources.The results show that the ionic liquid can increase the specific surface area of the catalyst(30?86 m2·g-1),and the boron can significantly improve the crystallinity of the metal particles.The catalytic activity of the catalyst is improved obviously by using oxygen as oxidant and solvent-free oxidation(the conversion of ethylbenzene is more than 50%).However,the relation of the catalytic activity of the catalyst with the content of ionic liquid is not at all linear,this may be due to the introduction of a large number of ionic liquid,resulting in generate other inactive species.At the same time,the distribution of active site is mainly concentrated in the edge of the carbon layer,which are easy to cause particle aggregation.Finally,we further explore the influence of calcination atmosphere on the apparent morphology and catalytic activity of the catalyst.The results show that the activation of oxygen has great effect on the structure of catalyst,which is beneficial to improve the catalytic activity.