Bergwerff Jaap A, Lysova Anna A, Espinosa-Alonso Leticia, Koptyug Igor V, Weckhuysen Bert M
Inorganic Chemistry and Catalysis Group, Department of Chemistry, Faculty of Science, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands.
Chemistry. 2008;14(8):2363-74. doi: 10.1002/chem.200700990.
An indirect magnetic resonance imaging (MRI) method has been developed to determine in a noninvasive manner the distribution of paramagnetic Co2+ complexes inside Co/Al2O3 catalyst extrudates after impregnation with Co2+/citrate solutions of different pH and citrate concentrations. UV/Vis/NIR microspectroscopic measurements were carried out simultaneously to obtain complementary information on the nature of the Co2+ complexes. In this way, it could be confirmed that the actual distribution of Co2+ inside the extrudates could be derived from the MRI images. By combining these space- and time-resolved techniques, information was obtained on both the strength and the mode of interaction between [Co(H2O)6]2+ and different Co2+ citrate complexes with the Al2O(3) support. Complexation of Co2+ by citrate was found to lead to a stronger interaction of Co with the support surface and formation of an eggshell distribution of Co2+ complexes after impregnation. By addition of free citrate and by changing the pH of the impregnation solution, it was possible to obtain the rather uncommon egg-yolk and egg-white distributions of Co2+ inside the extrudates after impregnation. In other words, by carefully altering the chemical composition and pH of the impregnation solution, the macrodistribution of Co2+ complexes inside catalyst extrudates could be fine-tuned from eggshell over egg white and egg yolk to uniform.
已开发出一种间接磁共振成像（MRI）方法，用于以非侵入性方式确定在用不同pH值和柠檬酸盐浓度的Co2+/柠檬酸盐溶液浸渍后，Co/Al2O3催化剂挤出物中顺磁性Co2+配合物的分布。同时进行紫外/可见/近红外显微光谱测量，以获取有关Co2+配合物性质的补充信息。通过这种方式，可以确认挤出物内部Co2+的实际分布可从MRI图像中得出。通过结合这些空间和时间分辨技术，获得了关于[Co(H2O)6]2+与不同Co2+柠檬酸盐配合物与Al2O(3)载体之间相互作用的强度和模式的信息。发现柠檬酸盐对Co2+的络合导致Co与载体表面的相互作用更强，并在浸渍后形成Co2+配合物的蛋壳分布。通过添加游离柠檬酸盐并改变浸渍溶液的pH值，可以在浸渍后获得挤出物内部Co2+相当罕见的蛋黄和蛋清分布。换句话说，通过仔细改变浸渍溶液的化学成分和pH值，可以将催化剂挤出物内部Co2+配合物的宏观分布从蛋壳型微调至蛋清型、蛋黄型再到均匀型。
