Surface and Catalytic Properties of Lanthanum-PromotedNi/Sepiolite Catalysts for Styrene Hydrogenation
Surface and Catalytic Properties of Lanthanum-PromotedNi/Sepiolite Catalysts for Styrene Hydrogenation
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DOI：
10.1006/jcat.1996.0074
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发表时间：
1996-03
影响因子：
7.3
通讯作者：
S. Damyanova;L. Daza;J. Fierro
中科院分区：
文献类型：
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作者：
S. Damyanova;L. Daza;J. Fierro
报道了La促进的两个系列镍/海泡石催化剂(xLaNi和NixLa)对苯乙烯加氢反应的催化性能。这两个系列都是通过两步浸渍法制备的，但在NixLa系列中先掺入La，然后加入镍，而在xLaNi样品中则相反。用程序升温还原(TPR)、氢气还原动力学、光电子能谱(XPS)和CO吸附红外光谱对催化剂进行了表征，以获得镍和镧在氧化和还原样品中的性质和分布的信息。还原动力学和XPS数据清楚地表明，Ni2+离子在xLaNi样品中与海泡石衬底作用较强，而在NixLa系列样品中作用较小。CO吸附在还原催化剂上的红外光谱表明，氧化镧对Ni/海泡石催化剂的促进作用使CO吸附结构的分布发生了变化。桥键物种的重建似乎是通过Ni(100)表面的形成而发生的。此外，CO可以以线性形式吸附在与氧化相接触的Ni原子中。桥联形式的减少和相对较高的还原镍物种浓度表明，La沉积在镍颗粒上，导致表面上有相邻镍原子的几率降低。所观察到的Ni7.1La催化剂稳定的最大活性不仅是由于La覆盖了较大比例的硅酸盐衬底，而且是由于沉积在其上的La_2O_3碎片隔离了Ni微晶表面的Ni原子。
The catalytic behavior for styrene hydrogenation of two seriesof La-promoted nickel/sepiolite catalysts (xLaNi and NixLa) isreported. Both series were prepared by two-step impregnations,but lanthanum was incorporated first and nickel afterward inNixLa series and the order was reversed inxLaNi samples. Thecatalysts were characterized by temperature-programmed reduction(TPR), kinetics of reduction by hydrogen, photoelectronspectroscopy (XPS), and infrared spectroscopy of adsorbed CO toobtain information on the nature and distribution of nickel andlanthanum in the oxidic and reduced samples. The kinetics ofreduction and XPS data indicate clearly that Ni2+ions interactstrongly with the sepiolite substrate inxLaNi samples and to alesser extent in NixLa series. The IR spectra of CO adsorbed onthe reduced catalysts demonstrate that the promotion ofNi/sepiolite catalyst with lanthana results in a change in thedistribution of CO-adsorbed structures. It appears thatreconstruction of bridge-bonded species occurs via formation ofNi(100) surfaces. Moreover, CO can be adsorbed in a linear formon Ni atoms which are in contact with oxidic phase. The decreaseof the bridged form and relative higher concentration ofunreduced nickel species gives an indication that lanthanum isdeposited on the nickel particles, leading to a decrease in theprobability to have adjacent nickel atoms on the surface. Theobserved stable maximum in activity for the Ni7.1La catalyst iscaused not only by covering by La a larger fraction of thesilicate substrate but also by isolating Ni atomson the surface of Ni crystallites by La2O3patches deposited on it.