Heterogeneous, gas-solid processes constitute an important class of catalytic reactions that play a key role in a variety of applications, such as industrial processing and environmental controls. Heterogeneous catalytic chemistry can be demonstrated in a simple heated flow reactor containing a fragment of the catalytic converter from a vehicular exhaust system. The reaction can be carried out under atmospheric pressure conditions, obviating the need for expensive and cumbersome vacuum equipment. The heterogeneous conversion of small molecules is easily monitored with a quadrupole mass spectrometer (QMS) of moderate mass resolution. While sampling at atmospheric pressure can normally be problematic, self-contained QMS instruments that utilize differential pumping are available and can be incorporated into the flow reactor. Combining these concepts and design ideas we have instituted an experiment for undergraduate chemistry students that illustrates concepts in surface science and catalysis while facilitating exposure to operational aspects of mass spectrometry and real-time monitoring of a process flow stream. (Contains 1 scheme and 2 figures.)