High-performance MnOx-CuO catalysts for low-temperature CO oxidation: metal interaction and reaction mechanism

Abstract

A series of MnO_x-CuO catalysts were fabricated by redox precipitation (MnCu-YH), hydrothermal (MnCu-SR), and oxalate complexation methods (MnCu-LH) for low-temperature CO oxidation. The results showed that the MnCu-YH achieved 100 % CO conversion at 175 ℃ with WHSV of 60000 ml/ (g·h). It was also observed that SO₂ could deactivate the catalyst, while H₂O could delay the toxicity. Through the characterization of HR-TEM, XRD, BET, it was found that MnCu-YH possessed a typical nanorod structure and the largest specific surface area, measured at 45.54 m²·g⁻¹. XPS and H₂-TPR analyses revealed that MnCu-YH had the highest ratio of adsorbed oxygen and Mn³⁺, and excellent redox capacity, which were due to the redox cycle formed by Mn ions and Cu ions (Cu⁺ + Mn⁴⁺ ↔ Cu²⁺ + Mn³⁺). This redox cycle could strengthen the metal interaction between Mn and Cu, which is the fundamental factor driving the strong CO oxidation activity of MnCu-YH. Besides, CO-TPD investigation showed that MnCu-YH has the most CO adsorption sites and is more likely to adsorb CO. A catalytic mechanism for CO oxidation was proposed depending on in-situ DRIFTS characterization. As the adsorption site of CO, Cu⁺ formed CO-Cu⁺ species, which reacted with surface reactive oxygen species to produce CO₂, and MnO_x participated in the reaction by changing its oxidation state to cause oxygen transfer.