Transition metal doped cryptomelane-type manganese oxide catalysts for ozone decomposition

- The different metal-ion-doped K-OMS-2 catalysts showed distinct differences in their ozone decomposition activity.
- Co3+ and Fe3+ replace the Mn3+in the cryptomelane structure and Ce4+ mainly replace the K+ in the tunnel and partially replace the Mn4+ in the cryptomelane structure.
- The morphology of Ce-OMS-2 is extremely different from the other M-OMS-2 catalysts.
- Ce-OMS-2 is promising for decomposing ozone under high-humidity conditions.
- The Mn3+content and number of surface defects play a key role during the decomposition of ozone.

Transition metal (Cerium, Cobalt, and Iron) doped cryptomelane-type manganese oxide (M-OMS-2) catalysts have been successfully synthesized and characterized. The different metal-ion-doped K-OMS-2 catalysts showed distinct differences in their ozone decomposition activity. Cerium-doped OMS-2 materials showed ozone conversion of 90% under RH = 90% and space velocity of 600,000 h−1. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) data suggested that the as-synthesized M-OMS-2 materials were all crystalline with no segregated metal oxide impurities. ICP-OES and XAFS results confirmed that Co3+ and Fe3+ replace Mn3+ in the cryptomelane structure and Ce4+mainly replaces the K+ in the tunnel and partially replaces the Mn4+ in the framework of the cryptomelane structure. Because of the differences in the substitution sites and the ionic radius of dopants, the morphologies of the catalysts were different. The Mn3+content and number of surface defects play a key role during the decomposition of ozone. Ce-OMS-2 is a promising catalyst for purifying waste gases containing ozone under high-humidity conditions.

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