SPECTROSCOPIC OBSERVATION OF A CATALYST SURFACE IN A REACTIVE ATMOSPHERE AT HIGH-PRESSURE

A PRINCIPAL objective in the study of heterogeneous catalysis is the determination of the structure and composition of solid surfaces under reaction conditions. Most applicable spectroscopic methods achieve surface sensitivity by detecting ejected electrons which have very short mean free paths in the solid1. But such measurements must be carried out in vacuum, whereas catalytic reactions are typically carried out at pressures of at least one atmosphere. Although such a gas environment can be penetrated by X-rays or neutrons, these probe the bulk properties of solids rather than their surf ace properties2-6. Here, we describe how a catalyst sample and its gas environment may be configured so as to constitute a photocathode ionization detector7. By monitoring the ionization cascade rather than photon absorption, we show that X-ray absorption spectroscopy can be used to examine monolayer amounts of adsorbate on the surface of a practical catalyst at one atmosphere pressure. The wider application of this technique to complex systems in a variety of environments has considerable potential for the study of heterogeneous catalysis, and may be extended to other areas of interfacial science.