Catalytic Ammonia Synthesis Over Metal-Free Silicon Disubstituted Cyclo[18]carbon: A Density Functional Theory Study

Area of Science:

• Computational Chemistry
• Materials Science
• Catalysis

Background:

• Nitrogen (N₂) activation and ammonia (NH₃) synthesis are crucial industrial processes.
• Developing efficient, metal-free catalysts is a key challenge in sustainable chemistry.

Purpose of the Study:

• To investigate silicon disubstituted cyclo[18]carbon as a metal-free catalyst for N₂ activation and NH₃ synthesis.
• To explore the catalytic mechanism and stability of the proposed catalyst using theoretical calculations.

Main Methods:

• Density Functional Theory (DFT) calculations at the ωB97XD/def2-TZVPP level.
• Systematic comparison of structural and electronic properties of various cyclo[18]carbon isomers.
• Analysis of reaction pathways, intermediates, and energy profiles for N₂ hydrogenation.

Main Results:

• The C₁₆Si₂(8) isomer was identified as the most stable configuration for catalysis.
• Dual silicon substitution created electron-deficient active sites, facilitating strong N₂ adsorption and activation.
• A stepwise hydrogenation pathway was elucidated, leading to NH₃ production via energetically favorable intermediates.
• A self-sustaining catalytic cycle was established, where the catalyst regenerates and re-enters the reaction.

Conclusions:

• Multisite silicon engineering of cyclo[18]carbon frameworks is a viable strategy for designing efficient, metal-free catalysts.
• The developed catalyst enables metal-free ammonia synthesis under mild conditions.
• Theoretical insights provide a foundation for experimental development of novel catalytic systems.