Abstract: Apparatus and process for real time analysis of the intermediates and products of a gas phase chemical reaction catalyzed by a particulate catalyst. Real time analysis is conducted under high vacuum using a detector contained within a high vacuum cheer. The reactor is connected to the vacuum chamber but is outside thereof, allowing the reactor to be operated either at high vacuum or under moderate pressure. Reactors and reactor feed manifolds of varying configuration may be interchangeably connected to the vacuum chamber on an essentially modular basis. Only a single vacuum system is required for the apparatus. Reaction products may also be analyzed by methods such as gas chromatography. Simultaneously with real time analysis of reaction products and intermediates, infrared, ultraviolet other reflected electromagnetic analyses may be conducted on the reacting gases or catalyst surface.