Characterization and activity of alkaline earth metals loaded CeO2–MOx (M = Mn, Fe) mixed oxides in catalytic reduction of NO

Abstract

Nanocrystalline CeO2–MOx mixed oxides (M = Mn, Fe) with different M/(M + Ce) molar ratio are prepared by sol–gel combustion method. X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Temperature Programmed Reduction with H2 (H2-TPR) and N2-adsorption (BET) analyses are conducted to characterize the physical–chemical properties of the catalysts. The activity of catalysts for reduction of NOx with ammonia has been evaluated. The CeO2–MnOx catalysts showed better low temperature activity than CeO2–FeOx. The superior activity of CeO2–MnOx with Mn/(Mn + Ce) molar ratio of 0.25 respect to other catalysts (with 83% NO conversion and 68% N2 yield at 200 °C) is associated to nanocrystalline structure, reducibility at low temperature and synergistic effect between Ce and Mn that are observed by XRD, TEM and H2-TPR. The CeO2–FeOx catalysts were found to be active at high temperature, being Ce–Fe the best catalyst yielded 82% NO conversion at 300 °C. The effect of alkaline earth metals (Ca, Mg, Sr and Ba) loading on the structure and catalytic activity of cerium mixed oxides are also investigated. Loading of Ba enhanced the NO reduction activity of mixed oxides due to the increase of number of basic sites. Highest performance with 91% NO conversion and 80% N2 yield attained over CeO2–MnOx (0.25)-Ba (7%) catalyst at 200 °C.