摘要
用X-射线衍射(XRD)、紫外-可见漫散射光谱(UV-VisDRS)、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。
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 of γ-Al2O3 when Ni^2＋ loading is far below its dispersion capacity on γ-Al2O3. Increasing Ni^2＋ loading, the ratio of Ni^2＋ ions incorporated into the octahedral vacancies of γ-Al2O3 increases. Since the octahedral Ni^2＋ ions are easier to be reduced to the metallic state, the reduction degree of supported NiO/γ-Al2O3 sample increases greatly with Ni^2＋ loading, thus resulting in a great increase in the CO uptake and catalytic activity of Ni/γ-Al2O3 catalyst for hydrogenation of α-pinene. The promotional effect of La2O3 on the catalytic activity of the supported Ni/γ-Al2O3 catalyst has been studied as well. It has been suggested that the dispersed La^3＋ species on γ-Al2O3 may inhibit incorporation of Ni^2＋ ions into the tetrahedral vacancies of γ-Al2O3 and increases the ratio of octahedral Ni^2＋ ions to tetrahedral Ni^2＋ 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.
出处
《无机化学学报》
SCIE
CAS
CSCD
北大核心
2007年第6期1021-1028,共8页
Chinese Journal of Inorganic Chemistry
基金
南京大学开放测试基金资助项目。
