Constructing α-MnO2/Mn2O3 heterojunction for formaldehyde oxidation.

Constructing heterojunctions with oxygen defect-rich structures and abundant phase interfaces poses an appealing yet challenging task in the development of non-precious metal oxide catalysts for formaldehyde (HCHO) oxidation. Herein, we present a simple and efficient method for fabricating highly active manganese oxide heterojunction catalysts for HCHO oxidation. This method involves the hydrothermal synthesis of a nanostructured α-MnO2/γ-MnOOH composite, followed by mechanical milling-induce phase transformation of γ-MnOOH to Mn2O3. Importantly, mechanical milling not only creates the heterojunction but also imparts oxygen defect-rich structures and an abundant phase interface to the catalyst. The resulting α-MnO2/Mn2O3 heterojunction exhibits outstanding performance in HCHO oxidation, comparable to the best non-precious metal oxide catalysts reported thus far. It achieves a 100% conversion of 100 ppm HCHO under a gas hourly space velocity of 120 L gcat-1 h-1 at 80 °C, corresponding to a mass-specific reaction rate of 8.92 μmol g-1 min-1 and an area-specific reaction rate of 0.18 μmol m-2 min-1. Based on the control experiments using in situ diffuse reflectance infrared Fourier transform spectroscopy combined with online gas chromatography, we gained insights into the mechanism of HCHO oxidation over the α-MnO2/Mn2O3 catalyst and the functional roles played by its component phases.