Atomic-scale imaging of catalytic surface reactions

Recent experimental work is reviewed showing that a field ion microscope (FIM) can also serve as an in situ catalytic flow reactor. A platinum field emitter (model catalyst, grain diameter > 200 A) exposes different small single-crystal planes with well-defined crystallographic orientations. The molecules reacting on the catalyst surface are also used as the FIM imaging gas. Due to preferential O 2 field ionization on O (ad) layers, different surface sites (O (ad) and CO (ad) ) can be discriminated in situ and in real time during the ongoing catalytic CO oxidation. The H 2 oxidation on a Pt field emitter is distinguished by a preferential imaging of catalytically active sites with the product molecule H 2 O (desorbed mainly as H 3 O + ). Isothermal, non-linear dynamic processes of CO- and H 2 oxidation reactions on Pt are investigated, involving the formation of face-specific adsorption islands, mobility of reaction/diffusion fronts and the creation of chemical waves. The electric fields in the FIM ( 1.5 V/A) appear to have a minor influence.