Catalysis: principles, progress, prospects.

In this introductory paper, we endeavour to bridge the gaps that currently exist between the three main subdivisions of catalysis: enzymatic, homogeneous and heterogeneous. Hitherto, there has been a tendency for each of these three divisions to grow separately using their own concepts, phrases and techniques. However, there is much that unites them, not least the notion of the catalytically active site and, in particular, its often unusual (constrained) state of electronic or atomic environmental disposition. We identify many points of similarity between, for example, the mode of action of, metalloenzymes on the one hand and the recent generation of transition metal ions embedded within nanoporous (usually siliceous) solids on the other. Useful unifying principles emerge from considerations of free-energy/reaction-coordinate plots. We present a number of tabulations and comparisons designed to facilitate the understanding of the mode of operation of existing, and the performance of new, catalysts. In doing so, we have drawn on our own work as well as that of others, including contributions that are to be found in this volume, with the intention of covering the great variety of catalytic phenomena.