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/gcata.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.