制备方法对煤焦油模型化合物裂解催化剂Ni/Al_2O_3结构及性能的影响

采用等体积浸渍法、浸渍沉淀法和机械化学法(市售载体和自制载体)制备了Cat-1、Cat-2、Cat-3和Cat-4四种催化剂,通过BET、H_2-TPR、XRD、XPS和NH_3-TPD等表征催化剂的结构特征,考察了各催化剂对煤焦油模型化合物甲苯和芘(3%,质量分数)裂解反应性能的影响。结果表明,四种催化剂均为介孔材料,且Cat-4的介孔有序度更高,比表面积最大,达235 m~2/g。Cat-4催化剂中,NiAl_2O_4尖晶石的还原峰面积最高,占总面积的85.2%,还原后Ni的分散度最大,粒径最小,约为10.0 nm,意味着活性位点多。实验表明,除Cat-1外,其他催化剂对芘的裂解活性基本相当,其中,Cat-4作用下的析碳量最低,为10.84%,经Cat-1、Cat-2和Cat-3裂解后,体系中的析碳量分别较Cat-4增加了35.0%、74.7%和45.7%。可见,机械化学法制备的催化剂不仅具有最高的比表面积利于活性组分分散,而且NiAl_2O_4尖晶石含量最高,可抑制裂解过程中积炭的生成,因而最适宜于甲苯+芘裂解体系。

Effect of preparation method on the structure and properties of coal tar model compound cracking catalyst Ni/Al2O3

Cat-1, Cat-2, Cat-3 and Cat-4 catalysts were synthesized via different preparation methods that are incipient wetness, impregnation-precipitation and mechanochemical method (carriers from market and homemade for comparison), and then characterized by BET, H₂-TPR, XRD, XPS and NH₃-TPD. The cracking behavior of toluene and pyrene (3%, mass fraction) (coal tar model compounds) were investigated to evaluate the catalytic performance of the stated catalysts. The catalyst characterization showed that the pore size of all the catalysts belonged to mesoporous range, and Cat-4 catalyst exhibited higher ordered mesoporous and larger surface area than others, up to 235 m²/g. Besides, the peak area of NiAl₂O₄ spinel reached up to the highest value of 85.2%. The dispersion of Ni in the reduced Cat-4 was the highest and its particle size was the lowest value, about 10.0 nm. Which means that there are more active sites. The catalytic performance results showed that the cracking rate of pyrene varied little for other catalysts, except for Cat-1, but the lowest carbon deposition of 10.84% was obtained under the action of Cat-4, while the carbon deposition of Cat-1, Cat-2 and Cat-3 increased by 35.0%, 74.7% and 45.7% respectively compared with that of Cat-4. Thus, Cat-4 prepared by mechanochemical method is more suitable for the cracking of toluene and pyrene system because of highest BET surface area, which is favorable for the dispersion of active component, and at the same time, the highest content of NiAl₂O₄ can inhibit the formation of carbon.