We present here the use of a simultaneous TGA/DSC thermal analyzer as a high-throughput reactor system to measure after calibration the heat of reaction and therefore the catalytic activity of heterogeneous catalysts in a fast, reliable and reproducible manner. By coupling the gas outlet of the analyzer with a mass spectrometer via a heated capillary additional data can be acquired. As a test reaction the oxidation of carbon monoxide with synthetic air, using Hopcalite and several transition and noble metals as catalysts, was chosen. The setup presented allows the rapid sequential screening of about 70 catalysts per day.