ORGANOMETALLIC CHEMISTRY AS A BASIS FOR UNDERSTANDING HETEROGENEOUS CATALYSIS

At the present time, our knowledge of the mechanism of action of most heterogeneous catalysts is limited. At the most primitive level, only the overall product distribution is known, while the nature of the catalyst-reactant interactions remains obscure. In a few cases, more detailed mechanistic proposals have been advanced, but they remain modest in scope compared to the detailed mechanisms that have been developed in molecular organic chemistry, and more recently, in organometallic chemistry. Indeed, even the apparently well-established catalytic mechanisms (for example, hydrogenation of olefins) are sometimes contested, indicating the fragility of the evidence on which these proposals are based. It must be recognized, however, that by comparison to strictly molecular systems, heterogeneous catalysts are intrinsically much more complicated. In addition, the application of physical methods to structural and mechanistic problems of heterogeneous systems, as well as interpretation of the results, can be difficult. A common problem encountered in heterogeneous catalysis is the complexity of the surfaces of solid catalysts. The so-called "active sites", a concept proposed by Sir H. S. Taylor [II. may be very small in number relative to the overall surface and, consequently