【摘要】 本文应用BET、气相色谱,红外光谱,竞争加氢反应和XPS等方法,分别考察了镧,铈、谱、钕的氧化物作为添加剂,对镍在γ-Al₂O₃表面的分散度、甲烷化活性、CO在镍上的吸附态以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金属镍的分散度和甲烷化活性,还可直按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经。更多还原

【Abstract】 Rare earths ( La, Ce, Pr, and Nd ) oxides have been used as additives to the Ni/γ-Al2O3 catalyst for methanation. Their effects on the dispersion of Ni atoms, methanation activity, state of adsorbed CO on the surface, as well as the electronic state of the Ni atoms have been examined using IR, XPS and competitive hydrogenation of toluene and benzene. The stretching frequency of the adsorbed CO was found to decrease, the binding energy of Ni 2 p3/2 was found to become lower, and the ratio of KT/B ( the relative adsorption coefficient of toluene and benzene ) was also found to decrase as the result of the addition of various rare earth oxides. These experimental findings all point to the conclusion that the electron density of the surface Ni atoms of the catalyst were increased. Thus, the rare earths oxides not only increased the dispersion of the Ni on the surface and the methanation activity as anticipated, but also directly affected the electronic state of the Ni atoms as well.This effect may be related to the decorating of the Ni particles on the surface by oxygen-deficient moieties, e.g. REOx, which are formed during the hydrogen treatment. The. interaction between the Ni atoms and the REOx, which lies in close proximity to the Ni crystallites, may result in transfer of electrons from the REOx to the Ni atoms.Effects of different magnitude were found for different kind of rare earth oxide. It is possible that this is intimately related to the fundamental properties of the rare earth oxide concerned. Preliminary results indicate that the variation of catalytic activity of methanation runs parallel to the variation of the ratio of the relative adsorption coefficient of toluene to that of benzene for catalysts with different rare earth additive when plotted versus the atomic number of the rare earth element.更多还原