Multiscale Simulation Guided Electric Field-Enhanced Ammonia Catalytic Cracking

Ammonia catalytic
cracking offers an efficient solution
for hydrogen
production, storage, and distribution, making it ideal for onboard
hydrogen generation in maritime propulsion systems when integrated
with fuel cells. However, conventional heating methods, even with
highly active ruthenium (Ru) catalysts, require high temperatures
to achieve satisfactory performance, posing a challenge for industrial
implementation. A promising strategy to address this limitation is
the application of strong external electric fields, which can lower
the temperature requirement through interactions between fields and
the dipoles of polarized species during ammonia cracking. To explore
such a field-dipole effect, we developed a multiscale simulation framework
that integrates density functional theory (DFT) calculations with
microkinetic modeling. This framework provides mechanistic insights,
identifies key rate-limiting steps, and optimizes conditions for field-enhanced
ammonia catalytic cracking over Ru. Our results show that at 673 K,
applying a −1 V/Å negative electric field dramatically
increases the turnover frequency from 0.03 s–1 (zero
field) to 1435.2 s–1. Similarly, at a higher temperature
of 823 K, the negative electric field enhances the turnover frequency
by 4 orders of magnitude compared to the no field conditions. In addition,
applying a −1 V/Å electric field reduces the operating
temperature from 750 K (zero field) to 586 K while maintaining a given
turnover frequency (e.g., 5 s–1). Sensitivity analysis
further identifies NH dehydrogenation over Ru(1013) as the rate-limiting
step across various electric fields and temperatures. This multiscale
model enhances the understanding of field-enhanced catalysis, offering
valuable insights into the development of more efficient hydrogen
production processes.