Infrared Spectroscopy and Catalysis Research

Abstract

The examples discussed here represent only a small part of the published work relating to infrared spectra of adsorbed molecules. The publications in this field indicate that infrared spectroscopy is being used for surface chemistry research in about 50 laboratories throughout the world. This effort is mainly devoted to problems related to catalysis, and in this field infrared spectroscopy is the most widely used physical tool for surface chemistry studies. The general acceptance of infrared spectroscopy is primarily due to the fact that it provides information which is pertinent to the understanding of surface reactions on an atomic scale. During the last decade significant progress has also been made in the classical chemical techniques of catalysis study and in utilization of physical tools which depend on phenomena of magnetism, conductivity, low-energy electron diffraction, and electron emission. Probably the most important progress has been in the field of inorganic chemistry, where dramatic advances have been made in knowledge of metal coordination compounds. Such knowledge is vital to the understanding of catalysis on metal surfaces. I believe this progress has produced an attitude of sophisticated optimism among catalysis researchers with regard to eventual understanding of heterogeneous catalysis. This attitude is closely related to the realization that there is no "secret of catalysis" which places catalytic action beyond the limits of ordinary chemical knowledge (22). This view implies that the chemical aspects of heterogeneous catalysis are not unique and that the use of solid catalysts merely provides a highly effective exposure of catalytic atoms and facilitates separation of the products from the catalyst. Many capable catalysis researchers believe that studies of homogeneous catalysis provide the most direct route for the study of heterogeneous catalysis. Obviously homogeneous reactions catalyzed by compounds containing only one or two metal atoms do not leave room for effects associated with crystal parameters or with electronic band structure characteristic of the metallic state. At present, I believe, it is more reasonable to concede that these solid-state factors may play a role of secondary importance than to completely exclude them from consideration. The view that catalysis involves only conventional chemistry carried out under complicated conditions gives grounds for optimism, since it limits the boundaries of the problem. However, it also imposes a limitation on what might be expected from fundamental catalysis research. Most fundamental catalysis researchers do not rest their hopes on a single dramatic discovery which will make it possible to predict in detail the best catalyst for any specific reaction. The idea that catalysis researchers work with this goal in mind is as unrealistic as the idea that workers involved in practical catalysis development select constituents for catalysts by throwing darts at the periodic table. Although the fundamental catalysis researcher does not expect to advance ahead of general chemical knowledge, he does hope that he will not continue to lag behind. Infrared spectroscopy has provided a significant step toward closing the gap.