Atmospheric Pressure Ammonia Synthesis via CO₂-Coupled Hydrogenation

Area of Science:

• Catalysis
• Chemical Engineering
• Materials Science

Background:

• The Haber-Bosch process, vital for agriculture, is energy-intensive and has a large carbon footprint due to high-pressure and temperature requirements.
• Intrinsic scaling relations limit traditional ammonia synthesis, hindering low-pressure and low-temperature approaches.
• Sustainable alternatives are needed to address the environmental impact of ammonia production.

Purpose of the Study:

• To develop a novel chemical looping strategy for ammonia synthesis at atmospheric pressure.
• To utilize carbon dioxide (CO2) hydrogenation as a trigger for ammonia production.
• To overcome thermodynamic limitations of conventional low-pressure ammonia synthesis.

Main Methods:

• A surface redox-mediated chemical looping strategy was employed using a cobalt-molybdenum bimetallic nitride (Co3Mo3N) as the nitrogen carrier.
• CO2 hydrogenation was used to dynamically alter the nitride surface, weakening Mo-N bonds.
• The process involved a redox cycle of surface oxidation and subsequent nitridation to regenerate the catalyst.

Main Results:

• Ammonia (NH3) was synthesized at atmospheric pressure, circumventing thermodynamic limitations.
• An unprecedented NH3 peak concentration of approximately 2.3% was achieved.
• A high NH3 release rate of 12.4 mmol·gcat−1·h−1 was observed at 500 °C.
• The CO2 hydrogenation acted as a chemical trigger, facilitating lattice nitrogen release.

Conclusions:

• Dynamic surface engineering can decouple kinetic and thermodynamic constraints in chemical reactions.
• This redox-mediated chemical looping offers a novel paradigm for sustainable nitrogen fixation.
• The strategy enables simultaneous carbon utilization and ammonia production, addressing environmental concerns.