A novel reactor system is described which permits ultrahigh‐vacuum surface spectroscopic studies and atmospheric pressure reactions to be done without a dedicated apparatus. An application of this system to studies of metal single crystals is shown, although its use for kinetic studies of such samples is limited in the present design. The reactor is used to study the surface properties and reaction characteristics of platinum deposited on a sapphire surface. The major use of the system is to study such model‐supported catalysts without exposing the sample to atmospheric contamination.