Catalytic Methanation Performance Over Highly Dispersed Ni-based Catalsyt In A Slurry-bed Reactor

CO methanation technology is the core in coal to synthetic nature gas（SNG）.It provides a new idea for the methanation process by using a slurry bed reactor,which can avoid a series of problems in a fixed bed reactor at the high temperature,such as catalyst sintering and carbon deposition.However,the industrial methanation catalyst exhibited poor catalytic activity and stability in a slurry bed,and thus it is urgent to develop a new methanation catalyst with high activity and stability at low temperature.The catalytic performance over the supported methanation catalysts could be affected by the metal dispersion,particle size and metal-support interaction.In this study,we focused on investigating the effects of ZrO₂ promoter,surfactant β-cyclodextrin and deposited carbon on catalyst physiochemical properties and structure and catalytic performance in a slurry bed reactor,in order to obtain a highly dispersed Ni catalyst.Combined with TEM,H₂-TPR,H₂ pulse chemical adsorption,N2-adsorption and desorption,powder XRD,in-situ XRD,TG-MS,XPS and CO-TPD techniques,to discuss the relationship between catalyst structure and catalytic performance for CO methanation.The conclusions are listed as follows:（1）Compared with the Ni/SiO₂ catalyst without ZrO₂ promoter,NixZr/SiO₂ catalysts modified with ZrO₂ promoter exhibited higher metal Ni surface area and dispersion,smaller nickel particle sizes and stronger interaction between Ni species and SiO₂ support and.Ni5Zr/SiO₂ and Ni10Zr/SiO₂ catalysts,with the ZrO₂ content of 5 wt% and 10 wt%,respectively,possessed optimal structure and physiochemical property.Under the reaction conditions of 300 °C,1.0 MPa and space velocity of 3000 mL·g-1·h-1,both catalysts showed similar and optimal CO conversion;Moreover,the catalytic stability were significantly improved.（2）On the basis of the preferred ZrO₂ content of 5 wt%,various contents of surfactant β-cyclodextrin was selected to modify the Ni-based catalysts.As the β-cyclodextrin content increased,the metal dispersion and surface area gradually increased,while the crystallite size and particle size gradually decreased.Ni5Zr/Si O₂-CD（1:5）catalyst with molar ratio of β-cyclodextrin and Ni of 1:5 showed the smallest crystallite size and particle size of nickel species,highest metal dispersion and largest active metal surface area and numbers of active Ni species.Under the conditions of 300 °C,1.0 MPa and high space velocity of 6000 mL·g-1·h-1,Ni5Zr/SiO₂-CD（1:5）catalyst exhibited optimal CO conversion and CH4 selectivity.（3）60 wt% glycerol aqueous solution was used as solvent to prepare the Nibased catalysts,which were then calcined and carbonized in an inert atmosphere.Compared with the catalyst calcined in air,the Ni-based catalyst carbonized with deposited carbon exhibited stronger metal-support interaction and larger amount of CO desorption,moreover,the dispersion of active Ni species increased from 3.3% to 7.1%,while the particle size of the Ni species increased from 30.7 nm to 14.2 nm.Under the conditions of 300 °C,1.0 MPa and high space velocity of 6000 mL·g-1·h-1,the conversion of CO and selectivity of CH4 reached ⁹3% and 91.4%,respectively,and the catalyst showed almost no deactivation in the reaction of 40 h.