The influence of silver on the structural, redox and catalytic properties of the cryptomelane-type manganese oxides in the low-temperature CO oxidation reaction

Cryptomelane-type manganese oxides modified with silver were prepared by the redox precipitation technique. The catalysts were obtained by the direct introduction of silver to the synthesis mixture containing manganese and the impregnation technique. The catalysts showed high activity in the low-temperature CO oxidation reaction. Studies of the nitrogen adsorption/desorption, powder X-ray diffraction, Fourier transform infrared spectroscopy in the photoacoustic mode (Fr-IR/PAS), and atomic force microscopy (AFM) evidenced strong influence of the preparation methods and the pre-treatment conditions on the structural and catalytic properties of the samples. It was found that the presence of silver in the synthesis mixture caused partial replacement of potassium ions in the tunnels, leading to the partial decomposition of the well ordered structure of the manganese oxides, increasing reducibility and activity of the catalyst. Structural changes were not observed in the samples prepared by the impregnation technique. Slight increase of activity of the impregnated samples was related to the increase of oxygen mobility. (c) 2007 Elsevier B. V. All rights reserved.