Co/γ-Al_2O_3催化剂上肉桂醛的选择加氢──催化剂的表征

Selective Hydrogenation of Cinnamaldehyde over Co/γ-Al_2O_3 Catalysts──Characterization of the Catalysts

采用XRD、TPR、XPS技术，分别研究了Co3O4／γ－Al2O3样品的晶相结构、还原性能及表面状态．XRD结果表明，不同前驱物的钴负载于γ－Al2O3后，钴是以Co3O4的结构存在，还原后的钴皆α－Co的形式存在，但以CoCl2为前驱物时，还原后的样品中钴的晶粒较大．TPR结果表明，负载于γ－Al2O3表面的Co3O4出现两个还原峰，这是因为负载于γ－Al2O3表面的Co3O4以晶柱与分散两种状态存在．随着钴负载量的增加，Co3O4的还原峰逐渐向低温移动，钴的还原更加容易．XPS表面分析结果表明，还原后，KCl在催化剂表面富集，覆盖了部分钴而使活性中心Co的数量减少，催化剂的活性下降．由于前驱物不同，使得催化剂表面钴的状态不同．以Co（NO3）2为前驱物的Co3O4／γ－Al2O3样品中，Co3O4与载体之间的相互作用较强；而以CoCl2为前驱物的Co3O4／γ－Al2O3样品，其Co3O4与载体之间的相互作用较弱．钴与载体间的强相互作用不利于肉桂醛分子中羰基的加氢．

Supported Co/γ-Al2O3 catalysts for cinnamaldehyde hydrogenation wcre prepared by impregnation from different precursors, Co (No3), and CoCl2, which were designated by the names of catalyst A and catalyst B.These catalysts were investigated using XRD, TPR and XPS techniques' Co3O4 phase was detected by XRD before reduction, and α-Co phase in both catalysts after reduction by hydrogen. As far as the phase structure of active cobalt was concerned, there was no difference between the catalysts prepared from different precursors.TPR results indicated that there are two species of Co3Co4on the support, namely, crystal1ine form and dispersed form. However, XPS revealed that the amount of Co0 in catalyst A is less than that in catalyst B after reduction. The results implied a stronger interaction between cobalt and γ-Al2O3 support in catalyst A, which is not advantageous to the hydrogenation of carbonyl group. Due to the introdUction of K+ from KOH precipitant, the activity of catalyst B is higher than catalyst A. The cobalt particles are larger after reduction, which is advantageous to selectivity. The combination of K+ and Cl- in catalyst B tesults in higher selectivity in hydrogenation of cinnamaldehyde to cinnamyl alcohol.