ABSTRACT
Electron microscopy (EM) techniques are very powerful and versatile research tools with which to investigate directly the local structure and chemistry of complex heterogeneous catalysts from the macroscopic to the atomic scale. Catalysts are generally heterogeneous (consisting of more than one element) and are increasingly nanoscale materials. In traditional approaches to exploring catalysts based on indirect chemical and spectroscopicmethods, results from large areas are averaged. Constructing models of the structure and mechanisms of the changing reactions over complex catalysts using such methods does not often provide satisfactory pictures of the process. Recent striking developments in EM methods have given the catalyst chemist methods for the direct visualization of the dynamic catalyst structure at the atomic level and the means for measuring its composition. EM of thin crystals pioneered by Hirsch et al (1977) and Cowley et al (1981) plays a pivotal role in materials science. There are detailed books on the principles of EM (Hirsch et al 1977, Cowley 1981, Eddington 1977, Williams and Carter 1996). In the following sections, we highlight some of the important principles in the study of heterogeneous catalysts. We describe some recent significant developments in EM methods including dynamical methods for studying catalysis. We outline the conditions necessary for obtaining the local atomic structure and chemistry of catalysts, their limitations and future trends.
