Laser-induced plasma and local temperature field for high-efficiency ammonia synthesis

The effective activation of chemically inert nitrogen under room temperature and normal pressure conditions has positive effects on the ammonia synthesis process. Herein, we propose a laser activated nitrogen to assist ammonia synthesis for the first time, which effectively activates nitrogen and facilitates the subsequent ammonia synthesis process. The nitrogen gas with a high bond dissociation enthalpy is ionized into nitrogen plasma on the local central region of catalyst tablet by pulsed laser, which can be controlled by the focused laser with high pulse energy but not be affected by the unfocus laser induced high temperature. Meanwhile, the ammonia synthesis is proceeded in the intermediate temperature annular region with Fe or iron nitride as catalyst, which is accelerated by pulsed laser produced nitrogen plasma. The laser-induced ammonia synthesis (LIAS) achieves the original ammonia yield of 70.8 μmol g−1 min−1 (28.32 μmol min−1) with a high hydrogen converting ratio of 9.5% by Fe as catalyst and a stable yield of 23.63 μmol g−1 min−1 (9.45 μmol min−1) with a hydrogen converting ratio of 3.2% by iron nitride as catalyst, which are 14.9 and 49.7 times than those of thermocatalysis using the same catalysts, respectively. As a precedent for laser-induced catalytic reactions, this work provides a perspective for nitrogen activation in the ammonia synthesis process.