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.