Heterogeneous catalysis by metals

Heterogeneous catalysis is a field with immense technological importance, forming the backbone of a variety of large-scale processes in the petroleum and chemical industries. In recent years interest in heterogeneous catalysis has spread to the automotive industry, and there has been a much increased interest among various groups concerned with extending fuel capabilities through processes such as coal gasification and liquefaction. Although many important technological advances based on heterogeneous catalysis have been made during the past half-century, there is a widely held view that understanding of catalytic phenomena is meager. It is true that heterogeneous catalytic processes are not generally understood in a detailed mechanistic sense. Moreover, there is no really fundamental understanding of why a given substance is, or is not, a good catalyst for a particular reaction. Nevertheless, there is evidence that real scientific progress has been made in studies of heterogeneous catalysis. For example, much has been learned about the nature of highly dispersed solids from studies on catalytic materials, particularly with regard to establishing the uniquely high dispersions obtainable by various techniques employed in catalyst preparation. Moreover, studies of chemisorption and catalysis on a wide variety of catalytic materials have provided a broad general understanding of the relationship between chemisorption ability and catalytic activity. Also, much progress has been made in recent years in establishing patterns relating the chemisorption ability or catalytic activity of an element to its position in the periodic table. These considerations form the basis for the discussion of heterogeneous catalysis by metals presented in this article.