High-precision synthesis of α-MnO2 nanowires with controllable crystal facets for propane oxidation

Abstract

Determining the effect of crystal facets on reaction performance is essential for designing an efficient propane oxidation catalyst. Herein, α-MnO₂ nanowires with exposed (110), (211), (310) and (200) facets were proposed, and their crystal facet-dependent reactivity to propane oxidation was investigated. The resultant α-MnO₂ nanowires with predominantly exposed (110) facets showed the maximum propane oxidation activity (T₉₀ = 262.1 °C), oxidation rate, and turnover frequency (at 230 °C), and high stability during the oxidation of propane. In situ diffuse reflectance infrared Fourier transform spectroscopy revealed that the oxidation to form carboxylates is the decisive step; therefore, the production of reactive oxygen species is very important. The results from density of states computations revealed that the lowest electron energy was present in the (110) facet, which helps in the generation of reactive oxygen species and the regulation of the surface valence of Mn. The characterization and calculation results indicated that the (110) facets are conducive to forming oxygen vacancies, which allowed the activation and adsorption of O₂ and propane, resulting in significantly enhanced propane oxidation activity. Apart from offering new insights about the structure–activity relationship of α-MnO₂ with different facets exposed for short-chain volatile oxidation reactions, this study proposes a technique that can be used for improving other manganese-based catalyst oxidation systems.