IR spectroscopy is a well-established method in the characterization of heterogeneous catalysts under reaction conditions. Working in transmission modes is the most common of currently applied technologies Yet, there are problems inherent in both methods (KBr wafers and self-supporting wafers) for the in-situ investigation of heterogeneously catalyzed reactions. These problems can be. avoided by using the DRIFT (diffuse reflection infrared Fourier transformation) spectroscopy. As is shown in this study, DRIFT spectroscopy proves to be a suitable method producing not only qualitative but also quantitative results of in-situ examinations of heterogeneous catalysts.