Tuning Reaction Pathway with Surface Metal Cocatalyst for Ethylene Production via Photocatalytic Methane Conversion

Area of Science:

• Catalysis
• Materials Science
• Sustainable Chemistry

Background:

• Photocatalytic oxidative coupling of methane (POCM) offers a sustainable pathway for converting methane (CH4) into valuable chemicals.
• Challenges in POCM include ambiguous reaction mechanisms and inefficient CH4 activation, limiting selectivity and production rates of hydrocarbons like ethylene.

Purpose of the Study:

• To investigate the photocatalytic oxidative coupling of methane (POCM) using palladium (Pd), gold (Au), and their alloy (PdAu) cocatalysts.
• To elucidate the reaction pathway and identify key factors for selective methane conversion into ethylene.
• To establish the critical functions of cocatalysts in methane valorization.

Main Methods:

• Utilized Pd, Au, and PdAu cocatalysts supported on TiO2 for POCM.
• Analyzed reaction intermediates and product selectivity to understand the reaction mechanism.
• Quantified methane conversion and ethylene production rates, and measured apparent quantum efficiency (AQE).

Main Results:

• The PdAu alloy demonstrated enhanced *CH2 generation and lowered the energy barrier for *CH2 coupling, promoting selective ethylene formation.
• Achieved an ethylene production rate of 0.18 mmol g-1 h-1 and a CH4 conversion rate of 13.73 mmol g-1 h-1 with PdAu/TiO2.
• Demonstrated an apparent quantum efficiency (AQE) of 12% at 350 nm, highlighting efficient light utilization.

Conclusions:

• Strong bonding between metal cocatalysts and *CHx intermediates is crucial for rapid and selective methane conversion.
• Effective cocatalysts must modulate CH4 activation, stabilize intermediates, and promote C-C coupling.
• Alloy engineering of cocatalysts, such as PdAu, is a promising strategy for advancing methane valorization into multicarbon products.