Catalytic performance of Mn/H-Beta catalyst modified by Ag for CH₄ combustion at low temperature

To improve the catalytic activity of Mn-based catalysts for CH₄ combustion at low temperature, the H-beta zeolites were employed as the support for Mn, and Ag was used as the cooperating agent for Mn/H-beta catalyst. Mn-Ag/H-beta catalysts were prepared by impregnation method. The combustion activity, H₂O resistance and SO₂ tolerance of Mn-Ag/H-beta catalysts were studied in a fixed-bed reactor at low temperatures between 523 K and 823 K. The interaction of Mn and Ag was investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Ag addition significantly promotes the catalytic performance of Mn/H-beta catalysts below 823 K. A Mn-Ag/H-beta catalyst with equal metal mass fraction of 6% has the highest activity for CH₄ oxidation. However, the activity of Mn-Ag/H-beta catalyst is inhibited in the presence of SO₂ and H₂O. No obvious promotion of H₂O for the formation of sulfate species is observed in the catalyst. Mn is mainly present in both the 3⁺and 4⁺oxidation states in Mn-Ag/H-beta catalysts. The presence of Ag enforces the transformation of certain amount of Mn³⁺ ions to Mn⁴⁺ ions. The major contribution of Mn suggested by the data in this paper is to stabilize Ag in a dispersed Ag⁺ state. This work is of considerable referential importance in the optimization design of catalysts for CH₄ combustion at low temperature.