Mechanistic Complexity of Methane Oxidation with H

Area of Science:

• Catalysis
• Materials Science
• Computational Chemistry

Background:

• Zeolites, particularly Fe/ZSM-5, are crucial catalysts in oxidation reactions.
• Understanding the active sites and reaction mechanisms is key to optimizing catalytic performance.

Purpose of the Study:

• To elucidate the mechanism of methane oxidation with H2O2 over Fe sites in Fe/ZSM-5.
• To identify the most favorable reaction pathway for C-H bond cleavage in methane.

Main Methods:

• Periodic density functional theory (DFT) calculations were employed.
• An extraframework Fe cluster [(H2O)2-Fe(III)-(μO)2-Fe(III)-(H2O)2]2+ was modeled within the zeolite pore.
• Three reaction mechanisms (heterolytic, homolytic, Fenton-type) were investigated.

Main Results:

• Fe sites activate H2O2, forming reactive Fe(III)-oxo and Fe(IV)-oxo complexes.
• Methane C-H bond cleavage occurs via heterolytic, homolytic, or Fenton-type pathways.
• The Fenton-type pathway exhibits the lowest activation barrier, leading to MeOH and MeOOH.
• H2O2 oxidation to O2 is more favorable than methane oxofunctionalization, limiting overall efficiency.

Conclusions:

• The Fenton-type reaction is the most efficient pathway for methane oxidation over Fe/ZSM-5.
• While C-H activation is feasible, the competitive oxidation of H2O2 reduces the overall yield of desired products.
• Further optimization is needed to enhance the efficiency of methane oxofunctionalization.