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Catalysis Looks to the Future
biochemistry and biomimetic chemistry,
chemical reaction engineering, and
chemical kinetics and dynamics.
Although research in catalysis is still dominated largely by experimental studies, theoretical efforts are becoming increasingly important. Theory provides a framework for understanding the relationships among catalyst composition, structure, and performance. The advent of supercomputers has made it possible to model a still larger body of catalytic phenomena and even, in some cases, to predict catalyst properties a priori. The availability of high-resolution computer graphics has proved particularly useful in visualizing the results of complex calculations and understanding the spatial relationships between catalysts and reactants on a molecular scale.
The industrial development of catalysts is an expensive and labor-intensive activity because catalysts currently cannot be designed from first principles. Rather, they must be developed via a sequence of steps involving formulation, testing, and analysis. An important aim of research in catalysis is to accelerate this process by providing critically needed knowledge and techniques. Another important function of research is to provide a reservoir of new information and materials that may contribute to the identification of new catalytic materials or processes. Thus, not only does research provide the tools and knowledge needed for direct facilitation of catalyst development, but it also increases opportunities for the discovery of new materials and new techniques.
One example suffices to illustrate the impact of research on catalytic science and technology. Because catalysis is a kinetic phenomenon based on the turning over of the catalytic cycle, the example deals with the prediction of overall kinetics for a catalyzed reaction based on a knowledge of elementary steps in the cycle. This information cannot be obtained theoretically at present, but it can be determined from experimental investigations. In the case of solid catalysts, some of these measurements are carried out on large single crystals, exposing one defined facet about 1 cm in size. These facets are nearly perfect in structure and are extremely pure. The chemistry of elementary processes occurring on such surfaces can be studied in great detail, to determine not only the rate of the process but also what intermediate species are formed. By studying different crystal facets, the effects of catalyst surface structure on reaction dynamics can be established. Information on the rates of elementary reactions can be assembled to describe the kinetics of a multistep process. This approach has been used to understand ammonia synthesis, over iron, and to establish which facet of iron is most effective in promoting this reaction. Such knowledge can be used to guide the preparation of industrial catalysts so as to expose the desired facets of iron preferentially. Recent studies have demonstrated that the best