Preparation Of Nitrogen-doped Graphene And Catalytic Performances Of Their Supported Catalysts For Oxidative Dehydrogenation Of Propane

Recently,Metal-free catalysts have attracted considerable attention,due to their low cost,high reliability,biocompatibility and sustainability.Graphene?RGO?has become a hot spot for research because of its ideal two-dimensionalcrystalstructureanduniquephysicalproperties.Nitrogen-doped graphene?N-RGO?is prepared by nitrogen-doped surface modification of graphene,which is superior to pure graphene.At present,it has difficulty to satisfy the demand of propylene that prepared by the conventional methods in the market,the production of propylene is short of demand.The oxidative dehydrogenation of propane to propylene is a highlight of catalysis research;the key is to prepare catalysts with good stability and high propene selectivity.The strong interaction between N atom and O₂ molecule can activate the molecular oxygen and enhance the activity of the catalyst.Therefore,the surface of graphene is modified to make it have better catalytic activity for oxidative dehydrogenation of propane.Pure NiO with the high conversion for oxidative dehydrogenation of propane is often combined with supports to form composite materials.Graphene has been an ideal material for NiO composite modification due to its good electrical property,partial defects and large specific surface area.In this paper,GO was prepared by Hummers method,then graphene was fabricatedbythethesolvothermalmethodorthechemical oxidation-reduction method with using GO as the precursor,and the influence of two methods on the structure properties of RGO was investigated.Finally,the solvothermal method was used to support NiO,and dope N atoms.A seriesofcharacterizationssuchasXRD,TEM,XPS,Raman,thermogravimetric analysis were carried out for a series of catalysts and the catalytic performance of oxidative dehydrogenation of propane was evaluated.Then the effects of feed gas velocity and alkane-oxygen ratio on the catalytic performance was investigated.The results of the study are as follows:1.Graphene was prepared by the chemical oxidation-reduction method with vitamin C as a reducing agent.The structure of graphene was intact when the dosage ratio of vitamin C to GO was 2:1 and ultrasound for 1 h.Using solvothermal method with ethanol as solvent,GO can be reduced to RGO at 160?for 12 h,and the operation process is simple.2.NiO/RGO catalysts were prepared by the solvothermal method.1%NiO/RGO catalyst gave 28.66%propane conversion at 28.08%selectivity for propylene,8.05%propylene yield when the feed of C₃H₈/air molar ratio of1:1,total feed flow rate of 40 mL·min^-11 and reaction temperature of 500°C.NiO is dispersed uniformly on graphene,and there is a certain synergistic effect between them.3.N-RGO catalysts were prepared by the solvothermal method,the feed of C₃H₈/air molar ratio of 1:1 and total feed flow rate of 60 mL·min^-11 over N-RGO???catalyst resulted in 31.64%propane conversion at 46.44%selectivity for propylene,the propylene yield can reach 14.69%at 500?.The propylene selectivity of 1%NiO/N-RGO???catalyst can reach 60.79%at low temperature,N-doped made the nano-layer structure of graphene more accumulate,and presented the tulle-like morphology of folds,which increased the defects of graphene.The strong interaction between nitrogen atom and molecules oxygen has futher enhanced the activation ability of molecular oxygen.Thus,the reaction activity was improved.