Ni2+在γ-Al2O3上的分散状态及负载型Ni/γ-Al2O3催化剂的α-蒎烯加氢活性

用X-射线衍射(XRD)、紫外-可见漫散射光谱(UV-Vis DRS)、程序升温还原(TPR)、CO化学吸附和微反测试等方法研究了Ni²⁺在γ-Al₂O₃上的分散状态和负载型Ni/γ-Al₂O₃催化剂的α-蒎烯加氢催化活性。结果表明，当Ni²⁺负载量远低于其在γ-Al₂O₃载体表面分散容量时，Ni²⁺优先嵌入载体表面四面体空位，随着Ni²⁺负载量的增加，嵌入载体表面八面体空位Ni²⁺的比例增大。由于八面体Ni²⁺易被还原为金属态Ni⁰，NiO/γ-Al₂O₃样品的还原度随Ni²⁺负载量的增加而大幅度地增加，经氢还原所得Ni/γ-Al₂O₃催化剂的CO吸附量和α-蒎烯加氢催化活性大幅度增加。对La₂O₃助剂的作用进行了研究，结果表明分散在γ-Al₂O₃上的La³⁺物种可阻止Ni²⁺嵌入γ-Al₂O₃表面四面体空位，增大了八面体Ni²⁺物种所占比例，提高了催化剂的还原度，故Ni-La₂O₃/γ-Al₂O₃催化剂催化活性高于Ni/γ-Al₂O₃催化剂。

Dispersion State of Nickel Ions on γ-Al2O3 and Catalytic Activity of Derived Nickel Catalysts for Hydrogenation of α-Pinene

The dispersion state of nickel ions on γ-Al2O3 and the catalytic hydrogenation activity of supported Ni/γ-Al2O3 catalysts have been studied by means of X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), H2 temperature-programmed reduction (TPR), CO chemisorption and microreactor tests. It has been shown that the supported nickel ions preferentially incorporate into the tetrahedral vacancies ofγ-Al2O3 when Ni2+ loading is far below its dispersion capacity on γ-Al2O3. Increasing Ni2+ loading, the ratio of Ni2+ ions incorporated into the octahedral vacancies of γ-Al2O3 increases. Since the octahedral Ni2+ ions are easier to be reduced to the metallic state, the reduction degree of supportedNiO/γ-Al2O3 sample increases greatly with Ni2+ loading, thus resulting in agreat increase in the CO uptake and catalytic activity of Ni/γ-Al2O3 catalyst for hydrogenation of α-pinene. Thepromotional effect of La2O3 on the catalytic activity of the supported Ni/γ-Al2O3 catalyst has been studied as well. Ithas been suggested that the dispersed La3 + species on γ-Al2O3 may inhibit incorporation of Ni2 + ions into thetetrahedral vacancies of γ-Al2O3 and increases the ratio of octahedral Ni2+ ions to tetrahedral Ni2+ ions, and thus increases the reduction degree of the catalyst precursor. As a result, the Ni-La2O3/γ-Al2O3 catalyst shows higher catalytic activity than the Ni/γ-Al2O3 catalyst with the same nickel loading.