CATALYZED CARBON GASIFICATION STUDIED BY SCANNING TUNNELING MICROSCOPY AND ATOMIC FORCE MICROSCOPY

Several important catalyzed gas-carbon reactions are studied by scanning tunneling microscopy (STM) and atomic force microscopy (AFM): C/H2/Pt, C/H2/Pd, C/O2/V2O5, C/CO2/K2CO3, and C/ NO/Rh. Single-crystal graphite is used as a prototype of carbon in the reactions. STM and AFM provide atomic resolution in three dimensions, making possible the direct identification of monolayer and multilayer structures on the reacted graphite surface. Reactions take place on the basal plane of graphite through monolayer and multilayer channeling, pitting. and edge recession. Therefore, by examining the etched surface structures of graphite after different reactions, reaction pathways and reaction parameters can be determined. It has been found that channeling is the primary contribution to the gasification rate in all these reactions. Two different modes of channeling are found. For reactions in C/H2/Pt, C/H2/Pd, C/O2/V2O5 systems, catalyst particles remain unchanged in size. Thus, the resulting channels either have constant-width or form zig-zag structures due to the changes of the motion of catalyst particles. However, for reactions in the C/CO2/K2CO3 and C/NO/Rh systems, wedge-shaped channels are produced. This indicates that the catalyst particles are shrinking in size, either because of volatilization or deposition of catalyst at the step edge. © 1993 Academic Press, Inc.