Catalytic manganese oxide nanostructures for the reverse water gas shift reaction

Abstract

Understanding the fundamental structure-property relationships of nanomaterials is critical for many catalytic applications as they comprise of the catalyst designing principles. Here, we develop efficient synthetic methods to prepare various MnO₂ structures and investigate their catalytic performance as applied to the reverse Water Gas Shift (rWGS) reaction. We show that the support-free MnO derived from MnO₂ 1D, 2D and 3D nanostructures are highly selective (100% CO₂ to CO), thermally stable catalysts (850 °C) and differently effective in the rWGS. Up to 50% conversion is observed, with a H₂/CO₂ feed-in ratio of 1 : 1. From both experiments and DFT calculations, we find the MnO₂ morphology plays a critical role in governing the catalytic behaviors since it affects the predominant facets exposed under reaction conditions as well as the intercalation of K⁺ as a structural building block, substantially affecting the gas-solid interactions. The relative adsorption energy of reactant (CO₂) and product (CO), ΔE = E_ads(CO₂) -E_ads(CO), is found to correlate linearly with the catalytic activity, implying a structure-function relationship. The strong correlation found between E_ads(CO₂) -E_ads(CO), or more generally, E_ads(R) -E_ads(P), and catalytic activity makes ΔE a useful descriptor for characterization of efficient catalysts involving gas-solid interactions beyond the rWGS.