Ammonia synthesis over γ-Al2O3 pellets in a packed-bed dielectric barrier discharge reactor

In this work, ammonia (NH3) synthesis from N2 and H2 was carried out in a packed-bed dielectric barrier discharge (DBD) reactor, while three kinds of commercial packing materials including acidic γ-Al2O3, alkaline γ-Al2O3 and neutral alumina pellets were employed. The effect of packing materials on plasma-assisted NH3 synthesis was investigated and compared with an unpacked DBD reactor. The results show that the presence of packing materials enhanced the plasma-assisted NH3 synthesis by 15.6% to 44.4% compared to the plasma reaction without a packing. The highest NH3 concentration of 1565.5 ppm was obtained over the alkaline γ-Al2O3 packed plasma reactor. The improvement of packing materials on plasma-assisted NH3 synthesis followed the order of alkaline γ-Al2O3  >  neutral γ-Al2O3  >  acidic γ-Al2O3  >  blank tube only. A series of characterizations were performed to illustrate the structure-performance relationships between plasma-induced NH3 synthesis process and packing materials. The results showed that the basicity of the packing materials played an important role in the plasma-assisted NH3 synthesis process. The reaction mechanisms of NH3 synthesis in the packed-bed DBD reactor were also discussed.