Study On The Novel High Surface Area Graphite Supported Ru-based Catalysts For Ammonia Synthesis

To improve the methanation resistance,high surface area graphite(HSAG)was adopted as a novel carrier of Ru catalysts for ammonia synthesis.Preparation methods,promoter content,and methanation of high surface area graphite were investigated in detail.Preparation methods,including impregnation,Mechnical mixing,and MOCVD were used to prepare Ba-Ru-K/HSAG ammonia synthesis with high activity and stability.The effect of preparation methods and carrier treatments on catalyst activity,stability and dispersion of ruthenium were characterized by N2 physical adsorption,XRD,H2-TPSR-MS,and transmission electron microscopy(TEM).The following main results were obtained:1.High surface area graphite is confiermed to be an alternative carrier for Ru-based catalyst.HSAG has high surface area,and at the same time,it still retains the full graphite crystal structure,which contributes to the catalyst activity and stability.Compared with activated carbon,HSAG has a relatively low specific surface area,but it's stacking plate holes and the perfect graphite structure benifits the dispersion of Ru precursor.2.Preparation methods,i.e.,impregnation method,dry mixing method,and MOCVD method,could achieve high activities of ruthenium-based ammonia synthesis catalyst with high surface area graphite as carriers.Following promoter content optimization,it's activity is similar to that of activated carbon supported catalysts.Furthermore,the promoter simplily introduced by mechanical mixing method also yields satisfactory activity.It is suggested that specific interactions between the precursor and the carriers play an important role in the improved activity and dispersion of Ru.3.High surface area graphite was still unstable under the ammonia synthesis conditions.It reacts with releaseing CH4 during operation.Stability of carbon depends on the graphitization degree.The order of methanation resistance for different carbon materials was:Graphite>High surface area graphite>Activated Carbon.The catalyst preparation procedure play negligible role in support methanation.High temperature treatment on carbon materials improves the stability.Heat treatment in hydrogen contributes to enhance C-C bond,strengthening saturation,weakening carbon methanation.Heat treatment in inert atmosphere improves the degree of graphitization,only at temperatures higher than 1400?,and the higher the processing temperatures,the better the stability of the carrier is.Calcination in air removes amorphous carbon from HSAGs,but it also plays a role in activation graphite.Thus there is few influence on the stability of high surface area graphite.