Non-thermal plasma catalytic ammonia synthesis over Ni catalyst supported on MgO/SBA-15

Non-thermal plasma (NTP) enabled ammonia synthesis is recently considered a sustainable technique as compared to the Haber–Bosch (HB) process. Herein we demonstrate the NTP catalytic ammonia synthesis in an dielectric barrier discharge (DBD) plasma reactor using mesoporous silica (SBA-15) supported Ni catalysts under ambient condition. Specifically, two types of MgO modified SBA-15 were developed (as the catalyst support) by the in situ doping and incipient wetness impregnation (IWI) methods, respectively. Experimental results demonstrated that the addition of Mg in SBA-15 via the IWI method favored the ammonia synthesis rate under NTP conditions. The developed Ni-Mg0.02/SBA-15-IWI catalyst exhibited the highest ammonia synthesis rate and energy efficiency value of 4.4 mmol h−1 gcat−1 and 1.05 gNH3 kWh−1, outperformed the Ni/SBA-15 and Ni-Mg0.02/SBA-15-In situ catalyst (i.e. the doping of Mg via in situ method). HRTEM and EDS mapping analysis showed that the addition of Mg (on SBA-15) via the IWI method favored the dispersion of Ni on the catalyst surface and the Ni-support interaction, i.e., uniform distribution of Ni nanoparticles of 5.1 ± 1.1 nm in the Ni-Mg0.02/SBA-15-IWI catalyst, which enhanced the ammonia synthesis performance. Finally, the developed Ni-Mg0.02/SBA-15-IWI catalyst displayed a slight decrease of ammonia synthesis rate from ~4.42 to ~3.89 mmol h−1 gcat−1 over a 40 h on stream, which could be attriburated to the aggregation of Ni particles based on the post-reaction HRTEM analysis.