Catalytic Reactions on Crystallites: Imaging and In-situ Chemical Probing at the Nanometer Scale

摘要

Most of the catalysts used in industry or in automotive pollution control are conditioned as a dispersion of small catalytic particles on a support of high specific area. Assuming a similar bulk composition, the extremity of a sharp metallic tip can mimic one of these catalytic particles. Field ion microscopy (FIM) is used to characterise these surfaces at the atomic scale at cryogenic temperatures and subsequently to image catalytic surface reactions at temperatures where they usually occur. Details of the 3D-particle morphology and the atomic-scale structure of individual planes are not easily accessible. By their size and their morphology, field emitter tips can be considered as models for a catalytic particle. A typical field ion micrograph is presented in figure 1a and is compared with a ball model given the form of a quasi-hemisphere (figure 1b). Every ball represents one single atom; those painted in white are the most protruding of the surface and appear bright on the field ion micrograph.