制备条件对Ni在Al_2O_3表面上的分配形态及Ni/Al_2O_3体系催化加氢性能的影响

用比表面和孔体积测定、XRD和程序升温还原(TPR)方法研究了一系列不同制备条件对Ni在Al_2O_3表面上的分配形态及其对CO加氢反应催化性能的影响.实验发现,本文所用制备条件对催化剂的比表面、孔体积及孔径分布无显著的影响.浸渍时间愈长,催化剂上能在较低温度下还原的物种愈少,催化剂上CO的加氢活性愈低;在浸渍前对载体作室温抽空处理后制得的催化剂上,Ni在Al_2O_3表面是高度分散的,这一高度分散物种易于在低温下还原,使该催化剂具有很高的CO加氢活性和生成CH_4选择性;载体的抽空温度及对载体加热均对Ni物种形态及其分配、催化剂性能有明显影响.

The Effect of Preparation Parameters on the Distribution of Ni Species and the CO Hydrogenation Performance of the Derived Ni/Al_2O_3 Catalysts

The effect of preparation parameters on the disribution of Ni species and the CO hydrogenation performance of the derived Ni/Al2O3 catalysts was studied by activity measurement, surface area and pore volume measurement, XRD, and temperature programmed reduction (TPR) methods. It was found that the impregnation time, degassing and heating pretreatment altered the distribution of Ni species and the performance of the derived catalysts. The surface area and pore volume did not change greatly with the different preparation conditions used. The amount of Ni species which could be reduced at about 570 K on Ni/Al2O3 decreased with increasing impregnation time, resulting in a decrease of CO hydrogenation activity. The degassing pretreatment at room temperature of the carrier could enhance the formation of Ni species which were highly dispersed and reducible at about 570 K, thus, the derived catalyst exhibited high CO hydrogenation activity. The nickel species which were reducible at about 570 K might be in the form of highly dispersed Ni2O3 and NiO monolayers, and crystallite of nickel oxides, and those which could be reduced at 870 K might be in the form of dispersed NiAl2O3 like species. The activity of Ni/Al2O3 depended not only on the metal dispersion, but also greatly on the chemical state of the active phase.