Preparation And Modification Of The Co Based Catalyst And Its Application In CO₂ Methanation

As an energy fuel,methane(CH4)is a component of natural gas,and widely applied to the industrial and for civil use,also,it is the chemical raw materials that used to produce syngas,ethyen,and ammonia.The industrial will not expand without the use of fossil fuels,which makes the content of the atmosphere CO2 increased sharply,therefore,how to reduce the content of CO2 in the atmosphere and its utilization has been the focus.CO2 methanation is considered an efficient method for CO2 conversion,which can not only reduce the concentration of CO2,but also makes up for the vacancy of natural gas.In this paper,the cobalt Fischer-Tropsch catalyst was used for CO2 methanation,the influence of the promoter doped into Co3O4 or the support on the catalytic performance were studied,and the following three aspects were included in the studies.Firstly,the Zr,Ce,or La modified Co3O4 catalyst were prepared with co-precipitation method and applied to CO2 methanation.The catalyst was characterized by XRD,the nitrogen adsorption/desorption,H2-TPR,CO2-TPD,XPS,and the IR spectra of pyridine adsorption(Py-IR).The results indicates that the C03O4 crystallite was decreased and the BET surface area was increased by doping Zr,Ce,or La,which would provide more active centers for the CO2 methanation.In addition,the introduction of Zr into Co3O4 formed an Co-Zr species,and reduced the outer-shell electron density of Co3+.Combined with the CO2-TPD and Py-IR results,Zr doped into the Co3O4 significantly increased the basic intensity of the weak and medium basic sites,as well as the amount of Lewis acid sites and Br(?)nsted acid sites.The Zr-Co3O4 catalyst exhibited the highest CO2 conversion(58.2%)and CH4 selectivity(100%)at 200℃ and 0.5 MPa with a gaseous hourly space velocity of 3600 mL·gcat-1·h-1.However,the stability of the four catalysts exhibited descendant in 20 h.Secondly,in order to improve the stability of the Co3O4 catalyst,the Co/TiO2 catalysts with different Co loading were prepared with deposition-precipitation method,and kept stable in 20 h.The results showed the Co/TiO2 catalyst with 20%Co loading amount(20%Co/TiO2)exhibited smaller crystallite size of C03O4.From the CO2-TPD,stronger medium basicity was observed on 20%Co/TiO2,which indicated more CO2 molecule were activated on the catalyst surface under 200-400℃.The activity test indicated that the CO2 conversion and CH4 selectivity was highest when using the 20%Co/TiO2.The 20%Co/TiO2 catalyst exhibited the highest CO2 conversion of 69.9%,and CH4 selectivity of 98.3%at 400℃,and kept stable in 20 h.Finally,the Y was used for improving the structure performance of TiO2 support.The results showed that the TiO2 crystallite was decreased and the BET surface area was increased by doping Y,resulting in the decrease of Co particle,and it also improved the dispersion of Co particle on the TiO2 support.The H2-TPR results indicated that the interaction between Co species and TiO2 was suppressed by doping Y into TiO2,therefore,more well-dispersed Co3O4 were reduced easily.Furthermore,the dopant of Y into TiO2 improved the amount of oxygen vacancies on catalyst surface,which would promote the activation of CO2.The activity test indicated that the CO2 conversion and CH4 selectivity was highest when using the 20%Co/2%Y-TiO2 catalyst.The 20%Co/2%Y-TiO2 catalyst exhibited the highest CO2 conversion of 85.9%,and CH4 selectivity of 99.5%at 350℃,and kept stable in 40 h.