MnO_x/ZrO_2 catalysts for the total oxidation of methane and chloromethane

摘要

Zirconia-supported manganese oxide catalysts prepared by wet impregnation and precipitation and calcined at 600 and 800 °C,respectively,in air were characterized by powder X-ray diffraction (XRD),textural investigations,temperature programmed reduction (TPR),temperature programmed oxygen desorption (TPD-O_2) and X-ray photoelectron spectroscopy (XPS) measurements.The catalytic activity was tested for the total oxidation of methane and chloromethane.The characterization studies showed clearly that both preparation methods result in samples with different supported MnO_x phases.Compared with the wet impregnation method higher amounts of nonstoichiometrically disperse MnO_x species were formed using precipitation method.The catalytic activity of the MnO_x/ZrO2 catalysts for the total oxidation of methane is influenced by the dispersity of the catalytically active MnO_x phase.In contrast to the methane oxidation the support zirconia itself indicates a high catalytic activity for the chloromethane conversion.Moreover,the total oxidation of chloromethane is connected with a catalyst deactivation and the formation of small amounts of higher chlorinated methanes as by-products at low reaction temperatures and chlorine.Nonstoichiometric surface basic chlorides (MnO_yCL,ZrO_yCl_z) are considered as the catalytically active phases for the total oxidation of chloromethane.