焙烧温度对共沉淀法合成Ni/Al_2O_3甲烷化催化剂性能的影响

采用并流共沉淀法制备Ni负载质量分数为15%的Ni/Al2O3催化剂,用于CO加氢甲烷化反应。结合紫外可见光漫反射、氢气程序升温还原、N2物理吸附-脱附和X射线粉末衍射等技术,考察焙烧温度对催化剂结构、活性与稳定性的影响。结果表明,低温(350-500)℃]焙烧的样品中活性组分Ni主要以孤立的Ni O物种和高分散的无定形Ni O物种存在,相应的还原态样品中Ni粒子尺寸较小,是其新鲜态样品低温活性较高的主要原因。800℃焙烧的样品中活性组分Ni主要以高分散的无定形Ni O物种和Ni Al2O4尖晶石微晶形式存在于催化剂表面,活性组分Ni与载体Al2O3间的作用力较强,稳定性较高,且经过800℃水热老化处理10 h后仍具有较大的比表面积(125 m2·g-1),是其具有较佳低温活性同时突显良好水热稳定性的主要原因。

Effects of calcination temperatures on methanation performance of Ni/Al2 O3 catalysts prepared by coprecipitation method

15wt%Ni/Al₂O₃ catalysts were prepared by the coprecipitation method and applied for CO methanation reaction.The effects of calcination temperatures on the structure,activity and stability of Ni/Al₂O₃ catalysts were investigated by the aid of ultraviolet visible diffused reflectance spectrum,hydrogen temperature-programmed reduction,N₂ adsorption-desorption and X-ray diffraction.The results showed that the main Ni species in the samples calcined at (350-500) ℃ were isolated and highly dispersed NiO,leading to smaller sizes of Ni crystal particles in corresponding reduced samples,which was the reason for the high activity of their fresh samples at low reaction temperature.The active component Ni species on the surface of the catalyst calcined at 800 ℃ were highly dispersed NiO and NiAl₂O₄ microcrystallite.The sample calcined at 800 ℃ provided stronger interaction between active component nickel and aluminum oxide,and possessed high specific surface area of 125 m²·g^-1 after enduring the hydrothermal treatment at 800 ℃ for 10 h,leading to its good activity and hydrothermal stability.