Copper-Manganese Composite Catalysts and Their Catalytic Mechanism

1. Overview of Copper-Manganese Composite Catalysts

Copper-manganese composite catalysts are a class of transition metal composite oxide catalysts that combine activity and economic efficiency. They belong to supported or composite oxide catalytic materials, with the core active component being a mixed valence state system of Cu⁰/Cu²⁺ and Mn²⁺/Mn³⁺/Mn⁴⁺. Compared with single-component Cu-based or Mn-based catalysts, they significantly improve catalytic performance through synergistic effects between components, and their cost is far lower than that of precious metal catalysts such as Pt and Pd. They are widely used in environmental protection and energy fields such as VOCs degradation, SCR denitrification, and CO oxidation, among which the Cu-Mn-Ce/molecular sieve system performs particularly well in the treatment of VOCs such as toluene.

2. Core of the Catalytic Mechanism

The high activity of copper-manganese composite catalysts stems from the synergistic effect of electronic effects and structural effects. From an electronic structure perspective, the multivalent characteristics of Mn (Mn²⁺↔Mn³⁺↔Mn⁴⁺) provide a channel for electron transfer, while charge transfer between Cu and Mn can regulate the position of the d-band center, optimizing the adsorption strength of reactants. The oxygen vacancies generated by the valence cycle of Mn can activate lattice oxygen, while Cu enhances the adsorption capacity of gas molecules, and the two synergistically accelerate the redox reaction.

Structurally, the composite system can inhibit particle aggregation, increase the specific surface area and pore volume, and increase the exposure of active sites. The active centers formed by lattice defects (such as Schottky defects), together with the strong interaction at the copper-manganese interface, constitute highly efficient catalytic sites. For example, in toluene oxidation, it can promote the complete cycle of toluene adsorption, C-H bond breaking, and desorption of oxidation products.

3. Preparation Methods and Typical Applications

Common industrial preparation methods include impregnation and co-precipitation.  Impregnation is widely used due to its simple operation. A typical process involves immersing a support (such as 5A molecular sieve) in a mixed solution of copper nitrate and manganese nitrate, followed by shaking, evaporation, and calcination at 500°C for 4 hours. This catalyst is primarily used in VOCs catalytic combustion (such as toluene degradation) and low-temperature SCR denitrification: in microwave-assisted toluene oxidation, a degradation rate of over 95% can be achieved at 230°C under 117W power; in the SCR reaction, its multivalent Mn species can promote the selective reduction of NO by NH₃.

4. Key Factors for Performance Regulation

Catalytic performance mainly depends on three factors: first, the Cu/Mn ratio, which needs to match the density of active sites and electron transfer efficiency; second, the support effect, where supports such as molecular sieves can improve dispersion and regulate pore structure, and the structure tends to stabilize after two microwave regeneration cycles; third, the calcination temperature, with 500°C being the optimal range, as excessively high temperatures can lead to sintering and deactivation. In addition, additives such as Ce can further increase oxygen vacancies and acid sites, strengthening the synergistic effect.

author: Hazel
date: 2025-12-05