Advancing ammonia synthesis under milder synthesis conditions, combined with efficient downstream separation, is essential for small-scale, distributed ammonia plants located near renewable sources. This study investigates the optimization of the reaction-absorption (RXN-ABS) process using a Cs-promoted, laser-induced graphene (LIG) supported 5 wt.% Ru-2.5 Cs(Cs/Ru molar ratio)/LIG catalyst, which achieves approximately 20,000 μmol g^-1h^-1 ammonia production at 350 °C and 1 MPa, outperforming traditional Ba-promoted catalysts at comparable conditions. Building on these catalytic results, we integrated the material into a reaction–absorption (RXN–ABS) process and explored its performance at 350 °C under pressures ranging from 1 to 3 MPa, systematically varying the compressor recycle ratio. Additionally, the influence of different salts (MnCl₂, MgCl₂, CaCl₂) loaded on different silica support supports (SBA-15, 200 µm silica, and graphite, aluminum, bentonite support) was systematically studied. Experiments demonstrated that increasing system pressure enhances ammonia production rates in RXN-ABS system, primarily due to elevated ammonia partial pressures that accelerate absorption kinetics and drive higher conversions, even at moderate temperatures. The RXN-ABS setup allowed for precise control of operational parameters, revealing that compressor (recycle) rate optimization is crucial. There exists an optimal point beyond which further increases yield diminishing ammonia production rates due to insufficient residence time and incomplete absorption. The process stability and cyclic performance of the reactor and absorber for long-term ammonia production at low temperature and low pressure were validated, showing consistent ammonia synthesis rates against the harsh experimental conditions. These results highlight the feasibility of using Cs-promoted Ru-LIG catalysts for efficient ammonia synthesis under mild conditions, underscoring the importance of integrated process parameter optimization for future scalable, distributed, and energy-efficient ammonia production systems.

Md Shahriar Rahman

Texas Tech University

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