Shape-dependency activity of Nanostructured α-Mn2O3 in direct synthesis of ethylene urea from CO2

Abstract

The direct conversion of CO₂ into high-value chemicals presents a sustainable pathway for greenhouse gas mitigation. While morphology-dependent catalytic activity has been widely explored in oxidation reactions, its role in CO₂-based urea synthesis remains uncharted. Herein, we systematically investigate the structure–activity relationship of shape-controlled α-Mn₂O₃ catalysts (nanosheets/NS, nanocubes/NC, nanooctahedrons/NO) for synthesizing ethylene urea (EU) from CO₂ and ethylenediamine (EDA). The Mn₂O₃-NS catalyst achieves record-breaking efficiency (96 % EDA conversion, 95 % EU selectivity in 20 min at 140 °C), surpassing all reported catalysts. Through combined XRD, XPS, CO₂/NH₃-TPD, and TEM analyses, we establish that the superior performance of Mn₂O₃-NS originates from its abundant surface oxygen vacancies (22.5 %) and more strong acid-base sites – features critically linked to its nanosheet morphology. This work not only provides fundamental insights into morphology-governed CO₂ activation mechanisms but also advances the rational design of manganese-based catalysts for industrial CO₂ valorization.