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Catalytic Resonance of Ammonia Synthesis by Dynamic Ruthenium Crystal Strain

Abstract

Ammonia affords dense storage for renewable energy as a fungible liquid fuel provided it can be efficiently synthesized from hydrogen and nitrogen. In this work, the catalysis of ammonia synthesis was computationally explored beyond the Sabatier limit by dynamically straining a ruthenium crystal (± 4%) at the resonant frequencies (10^2 to 10^5+ Hz) of N2 surface dissociation and hydrogenation. Density functional theory calculations at different strain conditions indicated that the energies of NHx surface intermediates and transition states scale linearly with that of the surface nitrogen on terraces, allowing the description of ammonia synthesis at a continuum of strain conditions. A microkinetic model including multiple sites and surface diffusion between step and Ru(0001) terrace sites of varying ratios for nanoparticles of differing size revealed that dynamic strain yields catalytic ammonia synthesis conversion and turnover frequency comparable to industrial reactors (400 ⁰C, 200 atm) but at lower temperature (320 ⁰C) and an order of magnitude lower pressure (20 atm).

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