Ambient Carbon-Neutral Ammonia Generation via a Cyclic Microwave Plasma Process.

Area of Science:

• Chemical Engineering
• Materials Science
• Plasma Physics

Background:

• Chemical looping ammonia synthesis offers a sustainable alternative to the Haber-Bosch process.
• Plasma-catalysis technologies are emerging for efficient gas activation.
• Pre-activation of dinitrogen (N2) is crucial for overcoming its high stability.

Purpose of the Study:

• To develop a novel reactor methodology for chemical looping ammonia synthesis using microwave plasma.
• To investigate the use of metallic iron catalysts for ammonia production.
• To elucidate the reaction mechanisms and kinetics under plasma-enhanced conditions.

Main Methods:

• Development of a microwave plasma reactor for pre-activating N2.
• Cyclical atmospheric pressure synthesis of ammonia using metallic iron catalysts.
• Density functional theory (DFT) calculations to model reaction pathways.
• High-resolution time-on-stream kinetic analysis and optical plasma characterization.

Main Results:

• Achieved ammonia synthesis rates of up to 420.9 μmol min-1 g-1 using iron catalysts.
• Identified both surface-mediated and bulk-mediated reaction domains influenced by plasma treatment time.
• DFT calculations revealed temperature-dependent nitrogen species distribution and equilibrium limitations.
• Observed generation of vibrationally active N2 and N2+ ions at lower bulk nitridation temperatures.

Conclusions:

• Microwave plasma pre-activation is effective for enhancing chemical looping ammonia synthesis.
• Metallic iron catalysts demonstrate potential for economical and environmentally benign ammonia production.
• Understanding transient nitrogen storage and plasma effects is key to optimizing catalyst performance.