Exsolution-Engineered Perovskite Catalysts for Durable Plasma-Assisted Ammonia Synthesis

Ammonia is a cornerstone chemical for global food security and an emerging carbon-free energy carrier, yet its industrial synthesis via the Haber-Bosch process remains energy-intensive and carbon-emitting. Non-thermal plasma catalysis offers a promising decentralized alternative for nitrogen fixation under milder conditions, though the long-term structural stability of supported metal catalysts under harsh plasma environments remains a key open challenge. Plasma-assisted NH₃ synthesis was investigated using exsolution-derived Co-La₂O₃/Al₂O₃ and Ni-La₂O₃/Al₂O₃ catalysts in a pulsed (1 kHz at 50% duty cycle) microwave reactor operating at sub-atmospheric pressure (2-6 Torr) and 2.45 GHz. The catalysts were prepared by reductive H₂ treatment of LaCoO₃ and LaNiO₃ perovskite precursors, deposited onto Al₂O₃ pellets, triggering metal exsolution and generating metallic Co⁰ and Ni⁰ nanoparticles embedded within a La₂O₃/Al₂O₃ matrix. Catalytic performance was evaluated across a range of H₂/N₂ flow rates (200-400 cm³/min each) and microwave power inputs (0.6-0.7 kW average), using bare Al₂O₃ as a reference. Co-La₂O₃/Al₂O₃ outperformed both Ni-La₂O₃/Al₂O₃ and the Al₂O₃ reference under all tested conditions, reaching a maximum H₂ conversion of 2.39% and a peak productivity of 20.6 μmol/g_cata.h, attributed to the finer metal dispersion and smaller nanoparticle size achieved during Co exsolution from the LaCoO₃ lattice. Post-reaction characterization by TEM, XRD and N₂ physisorption confirmed the structural integrity of both spent catalysts. No bulk phase transformations were detected by XRD, while specific surface areas were retained above 93% of the initial one. Metals' particle size slightly increased after plasma exposure, confirming the structural durability of catalysts. These results demonstrate that the exsolution mechanism confers meaningful sintering resistance under microwave plasma conditions, establishing exsolution-derived perovskite catalysts as a promising and durable platform for plasma-assisted nitrogen fixation.