Vacancy-enabled N₂ activation for ammonia synthesis on an Ni-loaded catalyst

Area of Science:

• Catalysis and Materials Science
• Chemical Engineering
• Sustainable Chemistry

Background:

• Ammonia (NH3) synthesis is crucial for fertilizers, traditionally relying on the energy-intensive Haber-Bosch process.
• Existing methods often use expensive ruthenium catalysts or face challenges in activating the strong nitrogen-nitrogen triple bond (N≡N).
• Strategies like promoter oxides and electride supports aim to lower activation energy but have limitations.

Purpose of the Study:

• To develop a stable and highly efficient catalyst for ammonia synthesis using earth-abundant elements.
• To investigate a novel dual-site mechanism for ammonia production that bypasses traditional scaling relations.
• To explore the potential of nitrogen vacancies in nitrides for activating atmospheric nitrogen (N2).

Main Methods:

• Synthesis and characterization of nickel-loaded lanthanum nitride (LaN) catalyst.
• Ammonia synthesis reaction kinetics and isotope-labeling experiments.
• Density functional theory (DFT) calculations to understand reaction mechanisms and nitrogen vacancy formation.

Main Results:

• Nickel-loaded LaN demonstrated stable and highly efficient ammonia synthesis.
• Nitrogen vacancies in LaN were found to have low formation energy, effectively binding and activating N2.
• The catalyst's performance, driven by distinct sites for H2 and N2 activation, rivals ruthenium-based catalysts and surpasses conventional Ni/Co catalysts.

Conclusions:

• Nickel-loaded lanthanum nitride offers a promising, cost-effective catalyst for ammonia synthesis.
• The study validates the use of surface nitrogen vacancies in catalytic cycles for N2 activation.
• This work introduces a new catalyst design concept for ammonia synthesis utilizing abundant materials.