Prepared Of ZrO₂-Al₂O₃ Mixed Composites And Catalysts For CO Methanation

Syngas methanation catalysts have been recognized as the most important part in the process of coal to SNG Ni/Al₂O₃ catalyst is the most employed for synthetic natural gas.However,under the condition of methane syngas process conditions?H₂/CO>3,300?600?,1?3 MPa?,Al₂O₃ as the supports for Ni catalysts will be transformed into boehmite in the presence of water-vapor produced in methanation reaction,consequently leading the structure of Ni catalysts into breakage,causing the particles sintering,and eventually resulting in catalysts deactivation.Composite oxides supports have relatively more stable structure,higher strength,and more hydrothermal stability than alumina supports.So according to the characteristics of methanation reaction,we doped Zr02 into Al₂O₃ supports in order to get the composite oxide supports with good hydrothermal stability,high structure stability and suitable specific surface area.This dissertation consists of the following Parts:preparation of the ZrO₂-Al₂O₃ composite supports with different ZrO₂ content by co-precipitation;investigation of the phase structure,specific surface area and hydrothermal stability of ZrO₂-Al₂O₃ composite supports with different ZrO₂ content;studies of the activity and stability of Ni/ZrO₂-Al₂O₃ in the process of the CO hydrogenation for CH4;studies of reasons of catalysts deactivation.ZrO₂-Al₂O₃ composite supports were prepared by co-precipitation using Al?NO3?3·9H₂O and Zr?NO3?4·5H₂O as raw material.The results showed that the ZrO₂ particles had a good disperse on the ZrO₂-Al₂O₃ composite supports and smaller particle size.Hydrothermal stability of composite oxides was dominated by the amount of solid solution and ZrO₂ coated effect.When the mass ratio of ZrO₂/Al₂O₃ was less than 0.24,the hydrothermal stability of the composite supports increased with the addition of ZrO₂;when the weight ratio of ZrO₂/Al₂O₃ was between 0.24 and 0.6,the hydrothermal stability of the composite supports got worse with the increase of the ZrOamount added;when the weight ratio was between 0.6 and 1.0,their hydrothermal stability enhanced.The Zr0.24Al sample had the best hydrothermal stability.The effects of calcination temperature on the crystalline structure,specific surface area,and hydrothermal stability of ZrO₂-Al₂O₃ composite oxides were investigated,and the results showed that:with the calcination temperature increasing,the hydrothermal stability of composite supports enhanced:The BET surface area varied as a function of calcination temperature for these supports.When the calcination temperature was 1100?,the ZrO₂-Al₂O₃ composite oxides had the best hydrothermal stability and suitable special area.10%Ni/ZrO₂-Al₂O₃ catalysts with different ZrO₂ content were prepared by impregnation and their reduction performance,textured structure and stability was studied,the results showed that ZrO₂ reduced the reduction temperature of catalysts;catalysts had a suitable surface area and good pore structure and the stability time of catalysts were the function of the hydrothermal stability of ZrO₂-Al₂O₃ support.The 10%Ni/Zr0.24Al catalyst had the longest stability time and lasted 178 h.The effects of different reaction conditions on the catalysts performance were investigated.The results showed that the reaction temperature effected the distribution of the product.When the reaction temperature was below 350? or above 400?,boudouard reaction increased,thereby reduced the yield of methane.Catalysts stability time was the function of reaction pressure.When the reaction pressure was 2.0 MPa,the stability time of the catalyst had reached more than 1000 h.Under the 12000 h-1 space velocity,catalysts rapidly lost activity.