Unique Phase Evolution and Multielemental Effects in Natural Rhodochrosite for Methane Oxidation

Rhodochrosite, a naturally occurring <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>MnCO</mml:mi> <mml:mn>3</mml:mn></mml:msub> <mml:annotation>${\rm MnCO}_3$</mml:annotation></mml:semantics> </mml:math> -based mineral with inherent compositional complexity, is investigated as a catalyst for methane oxidation. The material exhibits distinctive catalytic behavior, including enhanced <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>C</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:annotation>${\rm C}_2$</mml:annotation></mml:semantics> </mml:math> hydrocarbon formation and selective CO production, attributed to its multielemental composition and dynamic phase transformations under reaction conditions. In particular, rhodochrosite suppresses CO formation while enhancing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>C</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:msub><mml:mi>H</mml:mi> <mml:mn>4</mml:mn></mml:msub> </mml:mrow> <mml:annotation>${\rm C}_2{\rm H}_4$</mml:annotation></mml:semantics> </mml:math> production compared to pure <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>MnCO</mml:mi> <mml:mn>3</mml:mn></mml:msub> <mml:annotation>${\rm MnCO}_3$</mml:annotation></mml:semantics> </mml:math> , the primary component of rhodochrosite. Thermal treatment converts rhodochrosite into mixed manganese oxide phases ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>Mn</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:msub><mml:mi>O</mml:mi> <mml:mn>3</mml:mn></mml:msub> </mml:mrow> <mml:annotation>${\rm Mn}_2{\rm O}_3$</mml:annotation></mml:semantics> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>Mn</mml:mi> <mml:mn>3</mml:mn></mml:msub> <mml:msub><mml:mi>O</mml:mi> <mml:mn>4</mml:mn></mml:msub> </mml:mrow> <mml:annotation>${\rm Mn}_3{\rm O}_4$</mml:annotation></mml:semantics> </mml:math> ), while trace elements and mineral impurities are retained and may influence oxide phase evolution and catalytic behavior. These findings highlight the potential of natural multicomponent minerals as compositionally diverse, phase-adaptive platforms for selective methane conversion.