One-Step Synthesis of Ammonia Directly from Wet Air/N-2 by Plasma Combined with a gamma-Al2O3 Catalyst

The conventional Haber-Bosch NH3 synthesis process requires high temperatures and pressures, resulting in a high carbon footprint and the need to develop alternative NH3 synthesis methods. Accordingly, plasma-based and gamma-Al2O3-catalyzed NH3 synthesis from H2O (a hydrogen source) and air/ N2 (a nitrogen source) was studied under low temperature and low pressure conditions. The experimental results show that NH3 can be synthesized with air/N2 and H2O, although byproducts such as NO and N2O are also formed. The NH3 formation rate resulting from the use of N2 and H2O is higher than that of air and H2O. Increasing specific energy input (SEI) can increase the NH3 formation rate. Nevertheless, the energy efficiency of NH3 synthesis technology first increases and then decreases with SEI. An NH3 formation rate of 2.92 mu mol 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-1g-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 mu mol h-1 g-1) attained with N2 + H2O under an SEI of 11.50 J mL-1 and energy efficiency of 7.63 mg kW-1 h-1 (1.91 mg kWh-1g-1). Additionally, the gamma-Al2O3 catalyst exhibited good stability. Different results show that plasma-based and gamma- Al2O3 catalyzed NH3 synthesis technology is promising.