One-Step Synthesis of Ammonia Directly from Wet Air/N<sub>2</sub> by Plasma Combined with a γ-Al<sub>2</sub>O<sub>3</sub> Catalyst
Jiayu Feng, Ping Ning, Kai Li, Xin Sun, Chi Wang, Lijuan Jia, Maohong Fan
Abstract
The conventional Haber–Bosch NH 3 synthesis process requires high temperatures and pressures, resulting in a high carbon footprint and the need to develop alternative NH 3 synthesis methods. Accordingly, plasma-based and γ-Al 2 O 3 -catalyzed NH 3 synthesis from H 2 O (a hydrogen source) and air/N 2 (a nitrogen source) was studied under low temperature and low pressure conditions. The experimental results show that NH 3 can be synthesized with air/N 2 and H 2 O, although byproducts such as NO and N 2 O are also formed. The NH 3 formation rate resulting from the use of N 2 and H 2 O is higher than that of air and H 2 O. Increasing specific energy input (SEI) can increase the NH 3 formation rate. Nevertheless, the energy efficiency of NH 3 synthesis technology first increases and then decreases with SEI. An NH 3 formation rate of 2.92 μmol h –1 g –1 was achieved with an SEI of 11.68 J mL –1 and energy efficiency of 5.10 mg kW –1 h –1 (1.28 mg kWh –1 g –1 ), when wet air at a flow rate of 200 mL min –1 was introduced into the dielectric barrier discharge (DBD) reactor, which was lower than that (4.30 μmol h –1 g –1 ) attained with N 2 + H 2 O under an SEI of 11.50 J mL –1 and energy efficiency of 7.63 mg kW –1 h –1 (1.91 mg kWh –1 g –1 ). Additionally, the γ-Al 2 O 3 catalyst exhibited good stability. Different results show that plasma-based and γ-Al 2 O 3 catalyzed NH 3 synthesis technology is promising.