A REVIEW OF THE USE OF IN-SITU ELECTRON-MICROSCOPY TECHNIQUES FOR THESTUDY OF IRON-BASED CATALYSTS FOR COAL CONVERSION PROCESSES

We have used controlled atmosphere electron microscopy in conjunction with in situ electron diffraction in an attempt to learn more about th e fundamental aspects of iron-based catalyst particles used in coal li quefaction processes. This paper is devoted to a discussion of how the information derived from in situ electron microscopy examinations can be used to gain a unique insight into some of the factors which gover n the behavior of small catalyst particles. In this context, such feat ures as the morphological characteristics of the particles, catalyst d eactivation phenomena, and changes in the chemical nature of the parti cle as a function of reaction conditions are stressed. Attention is al so given to methods by which the activity of metal particles can be mo dified by incorporation of selected adatoms into the surface or pretre atment of the catalyst in certain gas environments. Emphasis is also p laced on the necessity to perform a suitable passivation step if one i s to maintain chemical integrity of a catalyst sample after exposure t o a reducing environment.