Effect of manganese or copper on catalytic properties of CeO₂-SiO₂ in the preferential oxidation of CO in excess of hydrogen (PROX-СО)

The work is directed to identifying the effect of copper or manganese oxide additives on the catalytic properties of the CeO₂–SiO₂ (CeSi) system containing silicon dioxide as a textural promoter in the preferential oxidation of carbon monoxide in excess hydrogen (PROX-CO). The CeSi catalyst was prepared by precipitation from salts in the presence of cetyltrimethylammonium bromide template, 5 wt % MnO_x/CeSi and 5 wt % CuO_х/CeSi were obtained by precipitation of modifiers from salts in the presence of potassium carbonate. The catalytic efficiency in PROX-CO increases in the series CeSi > Mn/CeSi > Cu/CeSi (at 200°C the time-averaged CO conversion values are 5, 19 and 78%, CO₂ selectivity values are 100, 65 and 59%). Characterization by X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption-desorption, Raman spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction with hydrogen demonstrated, that the presence of SiO₂ promotes the formation of highly dispersed and easily reduced CuOx clusters in close contact with CeO₂ particles, uniformly distributed over CeSi, and containing Cu⁺ adsorption centers. The Mn/CeSi system is characterized by an uneven distribution of manganese on the surface, a low number of MnO_x-CeO₂ contacts, and a low reduction ability of MnO_x in the low-temperature range (50–100°C).