Fundamental Studies of Metal Dispersion for Uniformly and Nonuniformly Distributed Catalysts

本项目的目的是通过对催化剂制备过程中浸渍步骤的基础研究，为预测催化剂的分散性提供科学依据。首先必须为这种新方法开发技术。实验设计中应尽量减少浸渍基本过程的耦合次数。因此，要研究的第一类系统将是平面基底上的吸附。高分辨率电子显微镜技术将采用特殊的“冷阶段”，以便在浸渍后直接，详细地观察催化剂前驱体的形态。第二种方案将设计用于强吸附系统，以允许从液相（通过原子吸附）测量吸附等温线，并直接从固相（通过化学吸附和可能的TEM）测量分散。第三个装置将被设计用来研究在非均匀分布的催化剂中分散随位置的变化。不同的一维分布曲线将产生在一个细长的催化剂样品中，包含足够的材料，使大块金属浓度和金属分散可以沿着样品长度的离散部分进行测量。在所有情况下，催化剂分散的直接测量将与现有的浸渍理论进行比较。最后，在需要时，将以这些相对简单的浸渍系统为基础，修订理论。这些研究旨在为催化剂体系制备程序的设计提供背景，这些程序将提供可预测的结果，而不是现在使用的试错方法。

The objective of this project is to establish a scientific basis for the prediction of catalyst dispersion from fundamental studies of the impregnation step of catalyst preparation. Techniques must first be developed for this new approach. Experiments will be designed in which the number of coupled elementary processes of impregnation is minimized. Thus, the first type of system to be studied will be adsorption over a planar substrate. A high-resolution electron microscopy technique will be employed with a special "cold stage" to enable direct, detailed observation of catalyst precursor morphology just after impregnation. A second scheme will be designed for strongly adsorbing systems to permit measurement of an adsorption isotherm from the liquid phase (by atomic adsorption) and measurement of dispersion directly from the solid phase (by chemisorption and possibly TEM) for the same catalyst batch. A third apparatus will be designed to investigate the variation of dispersion with position in nonuniformly distributed catalysts. Different one-dimensional distribution profiles will be produced in an elongated catalyst sample, containing sufficient material so that the bulk metal concentration and metal dispersion can be measured for discrete sections along the sample length. In all cases, direct measurements of catalyst dispersion will be compared to existing impregnation theory. Finally, revised theory will be developed where needed, using as a basis these relatively simple impregnation systems. These studies are intended to provide a background to design of catalyst system preparation procedures that would give predictable results, in contrast to the trial-and-error methods now in use.