Single-Atom Catalysts for Low-Temperature Thermocatalytic Ammonia Synthesis

Area of Science:

• Catalysis
• Materials Science
• Chemical Engineering

Background:

• Ammonia production relies on the energy-intensive Haber-Bosch process.
• This process has a significant carbon footprint.
• Single-atom catalysts (SACs) offer a potential alternative for milder ammonia synthesis.

Purpose of the Study:

• To review advancements in SACs for thermocatalytic ammonia synthesis.
• To explore how isolated metal sites alter catalytic pathways.
• To highlight strategies for optimizing SACs for efficient ammonia production.

Main Methods:

• Review of literature on SACs and sub-nanometric clusters for ammonia synthesis.
• Analysis of kinetic landscapes and active site environments.
• Discussion of various support materials (zeolites, carbons, ceria, MXenes) and metal-promoter interactions.

Main Results:

• Transitioning from nanoparticles to isolated sites favors associative N2 activation, lowering energy barriers.
• Ruthenium-based SACs on various supports demonstrate high NH3 productivities at milder conditions (200-400 °C, ≤30 bar).
• Emerging non-noble Fe and Co SACs rival or surpass Ru benchmarks, showing potential for cost-effective ammonia synthesis.

Conclusions:

• Tailoring metal site characteristics (number, coordination, support) is key to overcoming limitations in ammonia synthesis.
• SACs present a viable strategy for developing low-temperature ammonia synthesis processes.
• Optimized SACs can significantly reduce the energy demand and environmental impact of ammonia production.