The tortuous tale of the catalytically active site

The emergence of the concept of the active site in heterogeneous catalysts is traced from the early, tentative view of H.S. Taylor in 1925 to the structurally well-defined active site (at alpha TiCl3 prismatic faces) proposed by Cossee and Arlman in 1964. Comparisons are drawn between active sites in enzymes (as first revealed by the crystallographic work of D.C. Phillips in 1966), in homogenous (dispersed molecular) catalysts and those that occur in open-structure solids. The numerous advantages, both practical and of theoretical value, of single-site heterogeneous catalysts are outlined and illustrated with examples taken from those designed to facilitate regio-selective, shape-selective and enantio-selective conversions.