Ammonia Decomposition To Hydrogen By AC Arc Plasma

Hydrogen energy has been considered as an important approach for solving the environment issue. In recent years, ammonia decomposition reaction, as an in-situ hydrogen supply method, has been paid much attention. In this study, systematic studies were carried out to get insight into the AC arc discharge and electrode catalysis based on the energy efficiency of ammonia to hydrogen (ATH). The following results and conclusions were obtained:1. Discharge reactors with different structures showed different activity of ammonia decomposition. The activity of AC arc discharge reactor was significantly better than the dielectric barrier discharge (DBD) reactor. The ammonia conversion of AC arc discharge reactor reached about50%at input power30W. While only15%ammonia conversion was obtained with DBD reactor even at input power of80W.2. In situ optical emission spectrum (OES) revealed, the aboundant active spesies in AC arc discharge was NH-due to the higher electron density. However, the most active spesies in DBD was NH3*due to lower electron density. These indicated that the activation pathway between AC arc discharge and DBD may be different. These differences might be the reasons why the ammonia conversion in gas-phase AC arc discharge was higher than that in DBD.3. Tube-tube type reactor showed the best ammonia decomposition activity among the AC arc discharge reactors. Under the same input power, the steady state ammonia decomposition activityof tube-tube type AC arc discharge reactor followed the descending order Ni electrode reactor> SS electrode reactor> Cu electrode reactor. For SS and Ni electrode reactors, an obvious induction period of reaction activity was observed, but there wasn’t in Cu electrode reactor. Combined XRD characterization with on-line MS analysis, we found that the nature of the ammonia conversion induction period was the nitriding process of SS and Ni electrode surface. Choosing Cu electrode as the reference, the contributions of SS and Ni electrode surface catalysis in total steady state ammonia conversion were bothabout50%, the same contribution just like what the gas-phase plasma ammonia decomposition did.4. ATH energy efficiency was systematically investigated based on reactor parameters, discharge conditions, utilization of plasma heating and so on. Results showed that the ATH energy efficiency increased with decreasing the electrode diameter and electrode gap, reducing the discharge frequency and thermally insulating the reactor. When the8mm diameter reactor was insulated at the conditions of electrode diameter3mm, electrode gap4mm and discharge frequency5kHz, the ATH energy efficiency could reach12.5mol/kWh, which was higher than that obtained (6.1mol/kW·h (2g FeO)) in our previous work by plasma catalysis method5. In addition, the catalyst and pressure both had significant effect on the ATH energy efficiency in AC arc discharge reactor. When NH3flow was40-150ml/min, reaction pressure0.07-0.04MPa and0.2g10wt%Fe/fumed SiO2placed into the high volatge electrode’s high temperature zone, the ATH energy efficiency increased more than one time with complete ammonia conversion.