ATOMIC-SCALE IMAGING OF CATALYTIC SURFACE-REACTIONS

Recent experimental work is reviewed showing that a field ion microsco pe (FIM) can also serve as an in situ catalytic flow reactor. A platin um field emitter (model catalyst, grain diameter >200 Angstrom) expose s different small single-crystal planes with well-defined crystallogra phic orientations. The molecules reacting on the catalyst surface are also used as the FIM imaging gas. Due to preferential O-2 field ioniza tion on O-(ad) layers, different surface sites (O-(ad) and CO(ad)) can be discriminated in situ and in real time during the ongoing catalyti c CO oxidation. The H-2 oxidation on a Pt field emitter is distinguish ed by a preferential imaging of catalytically active sites with the pr oduct molecule H2O (desorbed mainly as H3O+). Isothermal, non-linear d ynamic processes of CO- and H-2 oxidation reactions on Pt are investig ated, involving the formation of face-specific adsorption islands, mob ility of reaction/diffusion fronts and the creation of chemical waves. The electric fields in the FIM (approximate to 1.5 V/Angstrom) appear to have a minor influence.