Programmable heating and quenching for efficient thermochemical synthesis.

Area of Science:

• Chemical Engineering
• Materials Science
• Reaction Engineering

Background:

• Conventional thermochemical synthesis methods struggle with temporal control, limiting reaction rate, selectivity, catalyst stability, and energy efficiency.
• Near-equilibrium conditions in continuous heating lack precise control over reaction temperature and time, hindering optimization of reaction pathways.

Purpose of the Study:

• To develop a non-equilibrium, continuous synthesis technique using pulsed heating and quenching for improved thermochemical reactions.
• To demonstrate enhanced selectivity, catalyst stability, and energy efficiency compared to conventional methods.

Main Methods:

• A programmable electric current was used to rapidly switch reaction temperatures between high (up to 2,400 K) and low states with short on-times (0.02 s) and longer off-times (1.08 s).
• The technique was tested using methane (CH4) pyrolysis as a model reaction and applied to ammonia (NH3) synthesis.

Main Results:

• Achieved >75% selectivity for value-added C2 products in CH4 pyrolysis, significantly outperforming conventional methods (<35% non-catalytic, <60% optimized catalysts).
• Demonstrated a stable and high synthesis rate of approximately 6,000 μmol gFe-1 h-1 for NH3 synthesis over >100 hours using a non-optimized catalyst at ambient pressure.

Conclusions:

• The pulsed heating and quenching technique offers a new model for highly efficient non-equilibrium thermochemical synthesis.
• This method provides temporal control, leading to superior selectivity, catalyst stability, and reduced energy costs.