While global warming becomes more and more tangible, joint efforts to decarbonize all human activities are intensifying. Among the sector that would benefit from carbon mitigation, the chemical industry holds a significant position. Beyond the fact it was responsible for 4.2% of the global CO2 emissions in 2019, 1.2% are attributable to the production of ammonia alone, making it one of the largest CO2 emitters of the chemical industry 1, 2. The main reason behind this considerable contribution is the fossil-based Steam Methane Reforming process (SMR) used to produce hydrogen, which is then fed to the Haber-Bosch (HB) process for NH3 synthesis. Furthermore, it is worth noting that half of the world’s food production currently relies on fertilizers produced with synthetic ammonia through this method, making it a critical challenge to tackle 3. Several alternative technologies have already been proposed and are currently being studied 4. Among them is the electrification of the H2 production, replacing SMR with electrolysis, which will have several implications on the process and will inevitably lead to new challenges 5. However, such a solution revolves only around the replacement of the SMR. Transitioning to a lower operating conditions process such as alkaline water electrolysis (60-90°C & 1-30 bar) can lead to the entire process being rethought, including the well-established Haber-Bosch technique (350-500°C & 150-300 bar). In this work, a novel technique is investigated to fully replace the HB process with a low temperature and pressure chemical looping process. Introduced in the early 20th century for hydrocarbon fuel conversion, the principle of chemical looping is based on the decoupling of a catalytic reaction in sub-reactions supported on a catalyst that passes through an intermediate state and is then regenerated in a loop. Nowadays, chemical looping emerges as a promising technology for various applications, including lowtemperature and pressure ammonia synthesis 6, 7. Among the recent studies on the subject, one demonstrated unparalleled NH3 production rates at mild conditions using Ni-BaH2/BaNH as a catalyst via reaction (1) and (2) 8. 4BaH2(s) +2N2(g) = 4BaNH(s) + 2H2(g) (1) 2BaNH(s) +4H2(g) = 2BaH2(s) + 2NH3(g) (2) Ammonia started forming at ambient pressure and temperatures as low as 100°C, with the synthesis rate reaching 3125 μmol g-1 h-1 at 300°C. Within the context of electrifying ammonia production, such low conditions would better match with alkaline water electrolysis. The present work provides an in-depth analysis of the behavior of Ni-BaH2 during nitridation (reaction (1)) under isothermal conditions. Parallel experiments were conducted on both N2 Temperature-Programmed Reaction (N2-TPR) and time-resolved in situ X-Ray Diffraction (XRD) to observe reaction (1) at 5 distinct temperatures ranging from 180°C to 300°C.
Dechany et al. (Mon,) studied this question.