MOF-derived metal oxide composite Mn2Co1Ox/CN for efficient formaldehyde oxidation at low temperature

Abstract

Metal oxide and metal oxide composites have drawn substantial attention owing to their potential as substitutes for noble metal catalysts for the oxidation of HCHO. However, there are several challenges in the development of their structures and morphologies to maximize their catalytic performance. Herein, an effortless and controllable strategy is reported for the synthesis of metal oxide composite catalysts by a mixed-metal approach and calcining bimetal MOFs [MnCo-BDC-DABCO], resulting in highly dispersed MnCoO_x nanoparticles encapsulated by N-doped carbon. Subsequently, a series of MnCoO_x/CN catalysts with different molar ratios of Mn/Co was applied for the oxidation of HCHO. The metal oxide composite exhibited better catalytic activity and lower apparent activation energy than the single metal oxide. 100 ppm of HCHO could be totally converted into CO₂ and H₂O at a temperature as low as 80 °C on the Mn₂Co₁O_x/CN catalyst. With a lower concentration of HCHO (∼10 mg m⁻³), this catalyst demonstrated enhanced catalytic efficiency and superior stability at room temperature. Additionally, it maintained approximately 100% conversion for 24 h and remained exceptionally stable even after three consecutive rounds of testing. The structures of the catalysts were confirmed via N₂ adsorption and desorption, TEM, H₂-TPR, XPS and in situ DRIFTS measurements to clarify their superb catalytic performance. The characterization results indicate that the growth of nanoparticles in Mn₂Co₁O_x/CN was hindered, generating small particles embedded in carbon with a high specific surface. Furthermore, the improved reducibility together with sufficient surface reactive oxygen species may be responsible for their excellent catalytic activity and stability. This MOF-templated strategy affords a practical way to prepare cost-effective and efficient metal oxide catalysts for application in the purification of indoor air.