大孔氧化铝表面原位生长镍基催化剂用于二氧化碳甲烷化

In-situ growth of nickel-based catalysts on the surface of macroporous Al_(2)O_(3) for CO_(2) methanation

大孔结构催化剂其有良好的传质、传热效果,于是可以减小反应过程的压力降和减缓热点生成。针对CO_(2)甲烷化强放热易导致催化剂活性组分烧结的问题以及对高空速下运行反应的需求,本文通过原位生长类水滑石(LDH)的方法在大孔氧化铝表面生成NiMgAl-LDH前驱体,制备出了高比表面积、大孔径和大孔容的Ni-MgO/Al_(2)O_(3)催化剂,研究了煅烧温度、还原温度和空速对催化剂结构及反应性能的影响。结果表明,通过调整煅烧温度来控制催化剂的物相组成,通过控制还原温度调节Ni的还原度和避免烧结,可提升还原后催化剂中Ni~0的活性位数量,从而提高其催化活性。其中,NiMgAl-LDH前驱体在400℃煅烧、650℃还原后制备的Ni-MgO/Al_(2)O_(3)催化剂具有最高的Ni活性比表面积,其对应的CO_(2)转化率和CH_(4)选择性也最优,显示提高Ni比表面积是催化剂性能提升的一个关键。此外,该催化材料在WHSV=80000 mL/(g·h)的高空速条件下仍能保持高催化性能,且具有优良的稳定性,在550℃下CO_(2)转化率保持在54%、CH_(4)选择性保持在79%。

Macroporous catalysts often exhibit excellent mass and heat transfer properties,which can reduce pressure drop and mitigate hot spot formation during the reaction process.Addressing the issues of the active component sintering due to the strong exothermicity of CO_(2) methanation and the demand for operation at high space velocities,in this work,a nickel-based catalyst with high surface area and large pore size and pore volume was prepared by in-situ growth of NiMgAl layered double hydroxide(NiMgAl-LDH)precursors on the surface of macroporous Al_(2)O_(3).The effects of calcination temperature,reduction temperature,and space velocity on the catalyst structure and reaction performance were investigated.The results demonstrate that the catalyst phase composition can be controlled by adjusting the calcination temperature,while the reduction degree of Ni is regulated by altering 0 the reduction temperature,which are effective in inhibiting the sintering of Ni,increasing the number of active Ni sites,and then enhancing the catalytic activity of Ni-MgO/Al_(2)O_(3).By conducting the calcination of NiMgAl-LDH precursor at 400℃and subsequent reduction at 650℃,the resulted Ni-MgO/Al_(2)O_(3) catalyst shows the highest active Ni surface area and exhibits the highest CO_(2) conversion and CH4 selectivity in the CO_(2) methanation,suggesting that the surface area of metal nickel is a crucial factor for the catalytic performance of Ni-MgO/Al_(2)O_(3).Furthermore,the Ni-MgO/Al_(2)O_(3) catalyst performs well at a high space velocity of WHSV=80000 mL/(g·h)and a good stability at 550℃,where the CO_(2) conversion and CH_(4) selectivity keep at 54% and 79%,respectively.