Experimental study on hydrogen-rich fuel generation via ammonia decomposition using a structured catalytic reactor†

Abstract

Thermo-catalytic ammonia decomposition has gained significant attention for its ability to produce a CO_x-free H₂-rich fuel. Due to the scalability advantages of structured reactors, this study experimentally evaluates the efficiency of a non-commercial stainless-steel monolithic Ru/Al₂O₃ catalyst to determine operating conditions for achieving practical partial conversion rates for applications such as dual-fuel engines. The analysis focuses on the effects of residence time and temperature on ammonia conversion, the heating value of H₂-rich gas, and the thermal energy required. The results show that higher temperatures and longer residence times significantly improve ammonia conversion, with conversion nearing completion observed at 600 °C and a flow rate of 50 mL min⁻¹. However, due to the low Ru loading on the monolith surface, ammonia conversion at 400 °C remained limited to 12%. Kinetic analyses revealed that achieving practical conversion rates above 60% with the catalytic reactor requires extending the residence time to 85 s at 500 °C. Additionally, supplying 50% of the input energy for a 200 kW dual-fuel engine using H₂-rich fuel would require only 37% of the available exhaust energy to meet the heating demand for ammonia decomposition at 400 °C with a 60% conversion rate. To further enhance the reactor's performance and scalability, targeted improvements such as optimizing catalyst loading, incorporating promoters, employing bimetallic Ru-based catalysts, refining reactor volume, and utilizing a parallel reactor configuration, could be explored to maximize efficiency and integration with practical energy systems.