Titanium-Based Hydrides as Heterogeneous Catalysts for Ammonia Synthesis

Area of Science:

• Materials Science
• Catalysis
• Inorganic Chemistry

Background:

• Nitrogen (N₂) activation and hydrogenation to ammonia (NH₃) is crucial for global food production.
• Transition metal hydride complexes are explored for N₂ activation, but catalytic NH₃ formation remains challenging.
• Titanium (Ti) and Tantalum (Ta) hydride complexes activate N₂, but not catalytically produce NH₃.

Purpose of the Study:

• To investigate the catalytic potential of solid-state hydride-containing titanium compounds for ammonia synthesis.
• To explore a novel pathway for ammonia production using non-precious metal catalysts.

Main Methods:

• Utilized solid-state hydride-containing Ti compounds (TiH₂ and BaTiO₂.₅H₀.₅) under elevated temperatures (400 °C) and pressures (5 MPa).
• Operated under continuous H₂/N₂ flow conditions for extended periods (∼7 days).
• Compared catalytic activity with conventional supported Ruthenium (Ru) catalysts.

Main Results:

• TiH₂ and BaTiO₂.₅H₀.₅ formed a nitride-hydride surface, continuously producing NH₃.
• Achieved catalytic activity up to 2.8 mmol·g⁻¹·h⁻¹, comparable to some supported Ru catalysts.
• Demonstrated the critical role of initial hydride presence for catalytic activity.

Conclusions:

• Solid-state titanium hydride compounds can serve as effective catalysts for ammonia synthesis.
• The initial hydride is essential, suggesting a hydrogen-based Mars van Krevelen mechanism.
• Introducing hydride into Ti expands the scope of heterogeneous catalysts, offering alternatives to precious metals.