Selective Methane Oxidation to Acetic Acid Using Molecular Oxygen over a Mono-Copper Hydroxyl Catalyst

Area of Science:

• Catalysis
• Materials Science
• Green Chemistry

Background:

• Acetic acid is a key industrial chemical, typically produced via multi-step processes involving methanol carbonylation.
• Current methods rely on precious metal catalysts and energy-intensive steps, driving the need for more sustainable alternatives.
• Methane, an abundant and low-cost feedstock, remains challenging to convert directly into valuable chemicals like acetic acid.

Purpose of the Study:

• To develop a direct, single-step catalytic conversion of methane to acetic acid.
• To investigate the efficacy of a novel single-site copper hydroxyl catalyst confined within a cerium metal-organic framework (MOF).
• To explore a milder and more environmentally friendly reaction pathway for acetic acid synthesis.

Main Methods:

• Synthesis of a mono-copper hydroxyl site catalyst confined in a porous cerium metal-organic framework (Ce-UiO-Cu(OH)).
• Direct conversion of methane to acetic acid using molecular oxygen as the oxidant under mild conditions (115 °C in water).
• Characterization using spectroscopic and theoretical studies, alongside controlled experiments to elucidate the reaction mechanism.

Main Results:

• Achieved high acetic acid productivity (335 mmol g_cat^-1) with 96% selectivity.
• Demonstrated a copper turnover number (TON) up to 400.
• Identified the reaction mechanism as oxidative carbonylation involving methane activation, carbonylation, and hydrolysis.

Conclusions:

• The Ce-UiO-Cu(OH) catalyst enables efficient, single-step conversion of methane to acetic acid under mild conditions.
• This approach offers a sustainable alternative to traditional multi-step industrial processes.
• The findings provide a foundation for designing heterogeneous catalysts using abundant metals for methane valorization.