La2O3对Ni/γ-Al2O3甲烷化催化剂的助催化作用

我国将稀土作为助剂引入镍基甲烷化催化剂,大大提高了催化剂的活性和热稳定性,并已投入工业应用［1－3］．稀土对不同镍催化剂反应性能及其作用机理的研究已有一些报导［3－7］．谢有畅等观察到镍负载在经单层La2O3改性的γ－Al2O3表面,其晶粒要比没有La2O3时小得多．Rotgerink等认为添加La后反应速率的增加不只是由于几何效应,而是La对甲烷化本身有促进作用,单位镍表面的活性是随La含量不同而改变的,活性增加的同时表观活化能也增加［5］．作为助剂的La2O3在氢还原和反应过程中的变化及其作用的研究和讨论较少,目前一般认为添…

Promoting Effect of La2O3 on Ni/γ-Al2O3 Methanstion Catalyst

The promoting effect of La2O3 on Ni/γ-Al2O3 methanation catalyst was investigated by XPS, TPR and TPD methods. Results indicated that La2O3 can be partially reduced to LaOx (x＜3/2) during H2 reduction of the Ni catalysts with La2O3.The excess charge associated with the LaOx can be transfered to Ni. It weakened C-O bond strength, accelerated CO dissociation, proportionation and methanation reaction. The interaction between NiO and Al2O3 can be suppressed and the formation of NiAl2O4-like species can be reduced by adding La2O3. With the increase of La2O3 contents the fraction of NiO which is easier to be reduced becomes larger. The fact that there was more residual H2 on the catalyst with La2O3 means that it is able to retain some H2. Besides, the distribution of CO adsorption sites of the Ni catalyst was shifted by adding La2O3.