镍基甲烷化催化剂中的助剂作用 Ⅱ重稀土氧化物添加剂的结构效应和电子效应

Role of Promoters in Ni Catalyst for Methanation (Ⅱ) Structural and Electronic Effects Caused by Heavy Rare Earth (Dy, Sm, Y, Eu,Yb,Tm, Gd, Er, Tb) Oxide Additives

应用ＢＥＴ、气相色谱、红外光谱、竞争加氢反应和ＸＰＳ等方法，在以前工作的基础上继续考察了Ｙ２Ｏ３、Ｓｍ２Ｏ３、Ｅｕ２Ｏ３、Ｇｄ２Ｏ３、Ｔｂ４Ｏ７、Ｄｙ２Ｏ３、Ｅｒ２Ｏ３、Ｔｍ２Ｏ３、Ｙｂ２Ｏ３作为添加剂，对镍在γ－Ａｌ２Ｏ３表面的分散度、甲烷化活性、ＣＯ在镍上的吸附态及表面镍原子的电子状态的影响．结果表明，稀土氧化物添加剂不仅明显地提高了金属镍的分散度和甲烷化活性，还直接地影响表面镍原子的电子状态．对不同稀土氧化物，这些效应各异．作者认为，利用稀土氧化物添加剂调节表面镍原子的电子状态，可能成为改进甲烷化催化剂活性的一个有效途径．

Heavy rare earth (Dy, Sm, Y, Eu,Yb, Tm, Gd, Er, Tb) oxides (REO x ) have been used as additives to Ni/ γ Al 2O 3 catalysts for methanation. Their effects on the dispersion of Ni atoms, methanation activity, state of adsorbed CO on the surfaces, as well as the electronic state of Ni atom have been examined using IR, XPS and competitive hydrogenation of toluene and benzene. The stretching frequency of the adsorbed CO was found to be decreased, the binding energy of Ni2P 3/2 was found to be lowered, and the relative adsorption coefficient of toluene and benzene ( K T/B ) were also found to be decreased as the result of the addition of various heavy earth oxides, which possibly caused the increase of electron density of the surface Ni atoms of the catalyst. Thus, heavy rare earth oxides not only increased the dispersivity of Ni on the surface and methanation activity as anticipated, but also directly affected the electronic state of Ni atom as well. This effect may be related to the decorating of Ni particles on the surface by oxygen deficient moieties, e.g. REOx, which are formed during the hydrogen treatment. Interaction between Ni atoms and REOx, which is in close proximity to Ni crystallites, may result in the transfer of electrons from REO x to Ni atoms. It is belived that application of rare earth oxide promoters to nickel catlaysts may be an effective route to improve their methanation activity.