Decoupling Kinetically Coupled Steps via Hierarchical Relay Catalysis on High-Entropy Alloy for Efficient Ammonia...

Area of Science:

• Materials Science
• Catalysis
• Chemical Engineering

Background:

• Ammonia (NH3) is a high-density hydrogen carrier, but its decomposition is kinetically limited at moderate temperatures.
• Existing Ruthenium (Ru)-based catalysts face challenges with N-H bond activation and hydrogen desorption.
• Coupled elementary steps in ammonia decomposition create scaling constraints for catalyst performance.

Purpose of the Study:

• To develop a hierarchical relay catalysis strategy for efficient ammonia decomposition.
• To design a multi-metallic high-entropy alloy (HEA) catalyst for improved kinetics.
• To overcome the limitations of traditional Ru-based catalysts in hydrogen production from ammonia.

Main Methods:

• Fabrication of a RuNiCoFeMo high-entropy-alloy (HEA) catalyst.
• Integration of distinct metallic centers (NiCoFe and Mo) to regulate elementary steps.
• Kinetic analysis, including reaction order measurements, to assess catalytic performance.

Main Results:

• The HEA catalyst demonstrated significantly enhanced NH3 and H2 reaction orders compared to monometallic Ru.
• NiCoFe sites facilitated N-H bond scission, while Mo incorporation weakened metal-H interactions.
• Achieved approximately 80% NH3 conversion at 450°C, a threefold increase in activity.

Conclusions:

• The hierarchical relay catalysis strategy effectively breaks scaling constraints in ammonia decomposition.
• The RuNiCoFeMo HEA catalyst offers superior performance by optimizing individual elementary steps.
• This approach provides a general design principle for complex catalytic reactions.