Density Functional Theory Study on the Reduction of NO by CO Over Fe₃O₄ (111) Surface

ABSTRACT

Iron or its oxides (Fe_xO_y) commonly exist in the ash of fossil fuel and biomass, and are used as oxygen carriers in chemical looping process, and Fe₃O₄ is a main occurrence. The NO reduction mechanisms by CO over Fe₃O₄ (111) surface was investigated via density functional theory (DFT) calculations. An optimized unit cell of Fe₃O₄ was constructed. The interaction between molecules and cell surface was described by the calculated adsorption properties and electronic structures. Results showed that the most stable adsorption of NO/CO belongs to chemisorption and NO has higher adsorption energy than CO. NO can be absorbed onto Fe₃O₄ surface to form (NO)₂ dimer structure, which easily decomposes via a small energy barrier. (NO)₂ dimer mechanism is a possible pathway for the reduction of NO by CO over Fe₃O₄, following three steps: 2NO → (NO)₂*, (NO)₂* → N₂O + O*, O* + CO* → CO₂. After the decomposition, the intermediate species N₂O molecule and the remaining O atom adsorbed strongly on the Fe₃O₄ surface can be removed by CO. CO also promotes the gaseous decomposition of N₂O. DFT results also showed O₂ will prevent NO reduction reaction. The calculated reaction rate constants further verify the existence of (NO)₂ dimer mechanism and the rate-limiting step is the removal of the surface O atom.

KEYWORDS:

• Fe₃O₄
• NO reduction
• catalytic effect
• DFT calculation

Acknowledgement

This work is supported by the National Key Development Project (2020YFB0606303) and National Natural Science Foundation of China (U1710251).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [U1710251]; National Key Development Project [2020YFB0606303]