不同金属改性Ni/KIT-6催化剂的制备及其甲烷化性能研究

采用共浸渍法分别制备了用Mg、Ce、V、La金属改性的Ni/KIT-6催化剂,用于CO_2甲烷化反应的研究。利用N_2吸附-脱附、X射线衍射、H_2程序升温还原、H_2程序升温脱附、透射电镜手段对催化剂进行了表征,考查了不同金属助剂对Ni/KIT-6的影响。结果表明,在KIT-6载体上活性金属和助剂的分散度都非常高,Ni粒子的分散度主要取决于KIT-6载体高度有序的介孔结构的限域作用,不受助剂金属添加的影响。各助剂金属的加入几乎不影响Ni/KIT-6催化剂的表面形貌,但对Ni金属还原的难易程度和还原度有影响。在研究的几种金属中,V金属使催化剂中Ni金属的还原最容易,还原度更高,且V金属的氧化物具有改变CO_2反应机理的作用,使得甲烷化反应进行的最好。用V改性后的催化剂与未改性的催化剂相比,CO_2的转化率提高了3.7%,CH_4的选择性提高了11.6%,CH_4的选择性达到了100%。

Preparation and properties of Ni/KIT-6 catalysts modified with different metals for methanation of CO2

Ni/KIT-6 catalysts modified by Mg, Ce, V and La for CO₂ methanation were prepared by co-impregnation method.The catalysts were characterized by N₂ absorption-desorption,XRD, H₂-TPD and TEM.The effects of different promoters on structure and properties of Ni/KIT-6 catalysts were investigated. The results show that the dispersity of Ni and promoters are very high. The dispersion of Ni particles depends primarily on the confinement effect of the well-ordered mesoporous structure of KIT-6, and is not affected by the addition of metal promoters. The addition of promoters does not affect the surface morphology of Ni/KIT-6 catalyst, but has effects on the difficulty and reduction degree of Ni reduction. Among the metal promoters studied, V addition makes the reduction of NiO in the catalyst easily and results in a high reduction degree. The oxide of V can change the reaction mechanism of CO₂ methanation, resulting in the best methanation performance. Compared with the unmodified catalyst, the catalyst modified by V makes the conversion of CO₂ and the selectivity of CH₄ increase by 3.7% and 11.6% respectively. The selectivity of CH₄ is 100%.