Enhancement of Catalytic Activities of Octahedral Molecular Sieve Manganese Oxide for Total and Preferential CO Oxidation through Vanadium Ion Framework Substitution

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Abstract

Abstract High‐valent vanadium ions were substituted into the synthetic cryptomelane manganese oxide (K‐OMS‐2) framework through a simple and low‐cost reflux method and investigated for total and preferential catalytic oxidation of carbon monoxide. Substitutional doping of V 5+ resulted in materials with modified composition, morphology, thermal stability; and textural, redox, and catalytic properties. The catalytic activity increased with V concentration until an optimum amount (≈10 % V incorporated) was reached, beyond that a structural “crash point” was observed, resulting in a material with low crystallinity, nanosphere morphology, and reduced catalytic activity. An increase in O 2 concentration in the feed gas resulted in an increase in conversion over 10% V K‐OMS‐2. This most active catalyst was deactivated by moisture only at low temperatures and showed better tolerance than undoped K‐OMS‐2. This catalyst also preferentially oxidized CO to CO 2 from 25 °C to 120 °C in large amounts of H 2 under dry conditions, without significantly affecting CO conversion. The doped catalyst also showed stable activity and selectivity in long‐run experiments. The mobility and lability of surface oxygen, formation of hydroxyl groups, and enhanced surface redox properties promoted by V doping were strongly correlated with the enhancement of catalytic activities of K‐OMS‐2 nanomaterials.

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