Abstract <p>The effect of the ratio of Ce and Mn oxides supported on cordierite ceramics on the structure and catalytic activity in the ozone decomposition reaction at room temperature was studied. The catalysts were prepared by impregnating cordierite ceramic blocks with citric acid at varying atomic ratios Ce : Mn. The physicochemical characteristics of the catalysts were studied using low-temperature nitrogen adsorption, X-ray phase analysis, scanning electron microscopy, and H₂ temperature-programmed reduction, and the catalytic activity of the samples in ozone decomposition was tested at high flow rate (20–50 L/min) and an initial O₃ concentration of 1–2 ppm. It has been shown that mixed oxide Ce–Mn catalysts are more active than catalysts based on individual Ce and Mn oxides. The activity passes through a maximum at the atomic ratio Ce : Mn = 1 : 2, which is due to the highly dispersed state of the supported oxides.</p>