制备条件对Ni/ZrO2-SiO2催化剂煤气甲烷化的影响

摘要

采用浸渍法制备了ZrO2-SiO2复合载体和Ni质量分数为6％的Ni/ZrO2 -SiO2催化剂,考察了载体制备时浸渍溶液pH值、焙烧温度和催化剂制备时的焙烧温度对Ni/ZrO2-SiO2催化剂煤气甲烷化反应性能的影响.采用X射线衍射、程序升温还原和扫描电子显微镜等方法对催化剂进行了表征.结果表明,载体浸渍溶液pH值为8.0 ～9.0,载体焙烧温度为550℃,催化剂焙烧温度为450℃时,Ni/ZrO2-SiO2催化剂在煤气甲烷化反应中显示了最优的催化性能,CO转化率100％,CO2转化率1.8％,CH4生成速率16.6 mmol/(h·g).进一步表征发现,制备ZrO2-SiO2复合载体时,增大浸渍溶液的pH值有利于形成粒径较小的亚稳态四方晶相ZrO2,可见四方晶相ZrO2更有利于甲烷化反应；载体焙烧温度会影响到NiO粒径的大小和其在催化剂表面的分散,温度过高和过低都会导致NiO粒径大小的不适宜以及分散性的降低；催化剂焙烧温度过高则会导致NiO与载体间的相互作用减弱,NiO分散性降低.%Ni/ZrO2-SiO2 catalysts with 6% Ni loading amount were prepared by impregnation. The ZrO2-SiO2 support was also synthesized by impregnation. Effects of pH value of the impregnating solution and calcination temperature of support and catalyst on activities of Ni/ZrO2-SiO2 catalysts were investigated. The catalysts were characterized using XRD,TPR and SEM measurements. Ni/ZrO2-SiO2(S5) catalyst exhibited excellent catalytic activity with 100% of CO conversion, 1. 8% of CO2 conversion and 16. 6 (mmol-h-1 -g-1) of CH4 formation rate. The preparation conditions were as follows: pH value of the impregnating solution, 8.0 ~9.0, calcination temperature of support and catalyst, 550 t and 450 °C. The mathanation activity of Ni/ZrO2-SiO2 was strongly influenced by the ZrO2 phase change. The catalyst with tetragonal zirconia showed higher catalytic activity. The increase of pH value of the impregnating solution was in favor of forming small tetragonal zirconia. The calcination temperature of support influenced the grain size and the dispersity of NiO, unsuitable temperature might lead to ill-fitted grain size and aggregation. Exorbitant calcination temperature could weaken interaction between NiO and the support, and lowered the dispersity of NiO.