Preparation Of High-loading Nickel-based Methanation Catalyst And Its Forming Technology Study

The extensive production and utilization of fossil energy not only leads to the accelerated depletion of fossil energy,but also brings serious air pollution problems,which has become an important factor restricting the sustainable development of society.Therefore,it is imperative to develop clean and efficient energy utilization technology.According to China’s energy structure and consumption characteristics,the development of coal-based synthetic natural gas has become one of the important ways to achieve clean and efficient utilization of coal.The core technology is methanation reaction process and synthetic catalyst.In this paper,the active components of nickel-based catalysts are easy to agglomerate at high loading,and the preparation method is complex,the utilization rate of raw materials is not high,and the industrialization process is difficult to achieve.Thus,a high Ni-loading Ni/Al catalyst was prepared by the anion-cation double hydrolysis methods for CO methanation.In addition,we also studied the effect of the addition of promoters Zr,Fe,Ce on the catalytic performance of the catalyst.At the same time,the precipitation mechanism of the prepared catalyst was discussed in the following.In addition,the high-temperature stability of the catalyst was improved by adding the promoter Mg.In order to meet the industrial application requirements and standards,the molding of the catalyst was studied by using the molding equipment.The results of the research will show as following:（1）The 40Ni-5M（M=Zr,Fe,Ce）/Al₂O₃ methanation catalyst was prepared by uniform coprecipitation method.The effects of the addition of additives on the low temperature activity and selectivity of the catalyst were investigated.The results show that:Under the reaction conditions of temperature 180-400 ^oC,pressure 1.0 MPa and mass space velocity of 20,000 mL?g^-1?h^-1,the addition of promoters Zr,Fe and Ce improved the activity and selectivity of the catalyst to varying degrees.In all catalysts,40Ni-5Zr/Al₂O₃ showed the best catalytic performance,and the CO conversion and CH₄ selectivity reached 99.9%and95.5%,respectively.（2）For the catalysts,their texture properties can be defined by means of a direct characterization analysis such as H₂-TPR,H₂-TPD,XPS,TEM and XRD reveals that the addition of Zr,Fe and Ce not only increases the dispersion of Ni on the surface of 40Ni/Al₂O₃,but also exposes more active sites of nickel.The ability of the catalyst to adsorb and dissociate H₂ is improved;the oxygen holes formed by the Zr species enhance the adsorption and dissociation ability of CO,reduce the energy barrier of the methanation reaction,and improve the reactivity and selectivity of the catalyst.The addition of Fe and Ce weakens the bond energy of the C-O bond,making the CO easier to dissociate,thereby increasing the catalytic activity.（3）The 40Ni-5Zr-xMg/Al₂O₃ catalyst was prepared by uniform co-precipitation method.The high temperature stability of the catalyst was improved by adjusting the amount of Mg doped.After optimization,40Ni-5Zr-30Mg/Al₂O₃ has higher activity and good stability.The optimal catalyst was tableted into a cylindrical shape of 5×4 mm,and the crushing strength was measured by a particle strength tester 665N/cm.In order to further increase the crushing strength of the particles,a pseudo-boehmite,methyl cellulose,and graphite were added,and other molding aids.The results show that different molding aids have different effects on the forming effect.The results show that 40Ni-5Zr-30Mg/Al₂O₃ is suitable for forming conditions:the water powder quality ratio is about 0.25.Determined the optimum molding water ratio parameter.