(344d) Programmable, Electrified, and Far-from-Equilibrium Thermochemical Reactions

Conventional thermochemical processes such as natural gas (CH₄) conversion and ammonia (NH₃) synthesis are often powered by fossil-fuel-based continuous heating, which are extremely carbon-heavy with severe CO₂ emissions. In addition, as the near-equilibrium continuous heating lacks rapid, precise and time-resolved control over the temperature profile (i.e., the reaction temperature and timescale), many reactions also suffer from poor selectivity, low yield, and/or poor catalyst stability. In this talk, I will present a novel far-from-equilibrium operating technique for thermochemical reactions (Nature 2022, 605, 470-476; Cover article) that employs programmable heating and quenching (PHQ) via electrification (i.e., Joule heating), which precisely controls the transient heating time (e.g., 20–110 ms) and provides rapid temperature quenching from up to 2400 K to near room temperature for gas phase reactants in milliseconds, resulting in improved selectivity, energy efficiency, and catalyst stability. Using CH₄ pyrolysis as a model reaction, our catalyst-free PHQ process enables high selectivity to value-added C₂ products (> 75% vs.< 35% by the conventional catalyst-free method, and vs. < 60% by most conventional methods with optimized catalysts) at a significantly lower energy cost (reduced by > 80%). Our PHQ process added a new dimension of tunability to thermochemical synthesis via the time-resolved temperature profile, which creates a unique opportunity for us to employ active learning to rapidly optimize any target product (e.g., C₂H₄) with much less experimental effort compared to conventional trial and error approaches. Beyond the homogeneous and endothermic CH₄ pyrolysis, we further demonstrate the utility of PHQ in NH synthesis, which is heterogeneous and exothermic. Under far-from-equilibrium conditions by PHQ, we achieve a stable NH₃ synthesis rate of ~6000 μmol/g/h under ambient pressure for over 100 h with a non-optimized Fe catalyst, which is among the highest even when comparing to literature reports utilizing optimized catalysts. We envision the PHQ technique can potentially address some of the most pressing issues in the chemical industry by enabling process intensification and decarbonizing the chemical manufacturing process using renewable electricity.