This paper describes a method to utilize DRIFT measurements with catalyst activity data in reaction kinetic analysis. The method is applied to construction and discrimination of reaction rate models for NO reduction with CO in the presence of oxygen over a Pd-containing three-way catalyst. DRIFT measurements have a special advantage to discriminate reaction rate models by comparing semiquantitative measurement of surface complexes to simulated surface coverages. Reaction kinetic models based on three different mechanisms (direct decomposition, bimolecular reaction, and N2O formation via isocyanate complex formation) were compared. Only minor differences between the models exist in the fitting of the models to measured gas-phase concentrations, whereas predicted surface coverages differ significantly from each other. The direct decomposition reaction model can most correctly predict the semiquantitative DRIFT measurements. Moreover, the explanation of the slow transient effects, detected on light-off experiments, was found by DRIFT measurements.