Abstract
Substituted Sr-ferrites Sr 1− x Ce x Mn 6− y W y Fe 4Al 2O 19 ( x = 0; 0.2; y = 0; 0.28; 0.56; 0.84) with the components ratio typical for Sr-hexaferrite obtained by co-precipitation and calcined at 700 °C have been characterized by thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and adsorption method. Ferrites have been studied in the selective catalytic reduction of NO by ammonia (SCR) using temperature-programmed desorption of ammonia (NH 3-TPD) and temperature-programmed reaction of ammonia (NH 3-TPR) techniques. It was shown that the substituted Sr-ferrites are multiphase. Its specific surface area is 27–59 m 2/g. Surface concentrations of elements in the samples differ from the bulk chemical contents. According to XPS data, the surface of the samples is enriched by strontium. The main components on the surface are in oxidized states: Sr 2+, Mn 3+, Fe 3+, Al 3+, Ce 4+ and W 6+. The surface acidity of the samples determined by NH 3-TPD increases from 0.023 to 0.071–0.082 mmol/g when Ce and W ions are introduced in SrMn 6Fe 4Al 2O 19. The most active (X NO ≈ 100%) and selective with respect to N 2 catalyst is the Sr 0.8Ce 0.2Mn 5.16W 0.84Fe 4Al 2O 19 ferrite obtained by the precipitation of the soluble nitrates of Sr, Fe, Mn, Al, Ce using ammonium para-tungstate and ammonium hydrocarbonate as precipitating agents. This sample is characterized by the highest surface acidity, the highest atomic ratio of [Mn]/[Fe] and the lowest oxygen reactivity.
Published Version
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