低镍催化剂上CO和CO_2加氢反应的对比研究

采用ＣＯ和ＣＯ＿２对比加氢活性测试，ＸＲＤ及ＴＰＲ方法研究了两个不同Ｎａ助剂含量的低镍Ｎｉ／Ａｌ＿２Ｏ＿３体系的性能。实验发现，在低镍催化剂上ＣＯ＿２在较低温度下就可加氢生成甲烷，而ＣＯ则需要更高的温度，ＣＯ＿２无需先经逆变换生成ＣＯ，然后再加氢，它可直接加氢生成ＣＨ＿４。在同一催化剂上，ＣＯ＿２加氢生成ＣＨ＿４的表现活化能要低于ＣＯ加氢生成ＣＨ＿４反应的表现活化能。晶相ＮｉＯ还原后形成的活性相对ＣＯ＿２加氢反应的活性明显高于它对ＣＯ的加氢活性，非晶相镍氧化物还原后形成的活性相对ＣＯ的加氢反应特别有利。Ｎａ助剂的含量不同会造成Ｎｉ氧化物物种的分配不同，从而导致ＣＯ、ＣＯ＿２的加氢活性及其随温度的变化也不相同，催化剂对ＣＯ、ＣＯ＿２加氢反应作用的本质是不相同的。

COMPARATIVE STUDY ON THE HYDROGENATION OF CO AND CO_2 OVER LOW NICKEL LOADING Ni/Al_2O_3 CATALYST

Two low nickel loading Ni/Al_2O_3 catalysts containing different amount of Na promoter havebeen characterized by comparative CO and CO_2 hydrogenation activity measurement, XRD and tem-perature-programmed reduction (TPR)techniques.It was found that CO_2 could be converted toCH_4 at lower temperature than that for CO.CO_2 could be converted to CH_4 directly without reverseshift reaction to form CO at first. when CO and CO_2 coexisted in a reaction system,CO inhibitedthe hydrogenation of CO_2 while CO_2 did not have significant effect on CO.The nickel species formedafter the reduction of crystalline NiO exhibited favorite hydrogenation activity for CO_2 which was higher than that for CO whithin the temperature range tested.While the nickel species formed afterthe reduction of noncrystalline nickel oxides which could be reduced at low temperature exhibitedhigh CO hydrogenation activity,and at above 540K thase species exhibited higher hydrogenation ac-tivity for CO than for CO_2 .The aparent activation energy for CO_@ hydrogenation was much lowerthan that for CO.The fact that Ni/Al_2O_3 catalyze both CO and CO_2 hydrogenation to form CH_4might be due to the inhomogeneity fo Ni/Al_2O_3.The active phase for CO hydrogenation and that for CO_2,and the interaction of CO with the active phase and that of CO_2 would be fifferent.