Hydrogen production via two-stage plasma catalytic decomposition of ammonia over Fe/ZSM-5 catalyst

Abstract

This study investigates a 2-stage ammonia (NH₃) decomposition process using nonthermal gliding arc plasma followed by thermal catalytic cracking. A 2-step catalyst preparation method was implemented, which included the ion-exchange and impregnation methods to achieve more homogeneous deposition of metal species on the zeolite support relative to the single-step impregnation method. The gliding arc discharge was sustained by an alternating current power source at 400 Hz. Plasma process parameters such as flow rate and NH₃ concentration were systematically varied to evaluate their impact on NH₃ conversion and hydrogen (H₂) production. Results indicated that the optimal conditions for plasma-based H₂ production were achieved at a flow rate of 4.5 L/min and an NH₃ concentration of 11% in nitrogen (N₂), yielding an H₂ production of 14.5 g/kWh. Further, the thermal catalytic NH₃ decomposition revealed that the catalyst prepared using the combined ion-exchange and impregnation method was superior to those prepared via individual methods. It was observed that although a higher conversion was achieved with the combination of plasma, the energy required was high. Also, the catalyst itself was capable enough at higher temperatures, achieving around 92% conversion at 700 °C. Thus, additional energy used for plasma is not essential at high temperatures, suggesting that the plasma stage can be beneficial at low temperatures or as a preheating stage of the catalyst.