New microcrystalline catalysts

Abstract

Owing to recent developments there is now a prodigality of crystalline inorganic solids capable of catalysing the chemical conversions of numerous gaseous molecules, especially hydrocarbons. Very many of these new catalysts are microporous and microcrystalline, and have their accessible active sites distributed uniformly throughout their bulk. They are, therefore, amenable to investigation by essentially all of the premier experimental and computational tools of solid-state physics and solid-state chemistry. The deployment of these tools has yielded fresh insights into the mechanisms of catalytic action and also suggested new strategies, some of which have already been tested, for the design of specially tailored selective catalysts. The benefits of multi-pronged approaches to the investigation of the reactivity of catalysts, made possible by the combined use of intense X -ray sources (both laboratory-based and synchrotron radiation) and supercomputers, are illustrated by specific reference to zeolitic solids that contain cages and channels of molecular dimension. Such crystalline solids, either in their highly acidic or metal-ionexchanged forms, are of great practical value on an industrial scale. They are also ideally suited for in situ exploration of the subtle structural changes that accompany, or are responsible for, the activation and deactivation of catalysts. Ways of optimizing the performance of catalysts, including the possible construction of ‘teabag’ analogues, and of coping computationally with their properties and performance so as to deepen our understanding of their mode of operation are outlined with reference to both the zeolites and the ever-widening range of solid oxides crystallizing with pyrochlore and perovskite structures.