Synthesis of ammonia under an electric field using lanthanum-based catalysts

Abstract

The use of ammonia as a hydrogen carrier is a fast-growing research area due to ammonia’s high weight percentage of H₂ (17.6 %) and its safer to handle features. Therefore, a higher demand for ammonia in energy applications is expected in the near future. Electric field-assisted ammonia synthesis is one way to meet the growing demand for ammonia, both for energy purposes and for industrial applications, mainly in fertilizer production. This study highlights the use of electric current for ammonia production by using NiO/La₂O₃ catalysts in a fixed-bed flow reactor. The operating conditions were maintained at a pressure of 5 bars and a current of 9 mA. The catalytic activity was analyzed in terms of ammonia concentration (ppm), synthesis rate $R_{{\mathrm{NH}}_3}$(µmol.min⁻¹.g_cat⁻¹) and energy efficiency EE (g-NH₃ [kWh.g_cat⁻¹]⁻¹). Good catalytic activity was obtained at 200 °C for the 10 wt% NiO/La₂O₃ catalyst, with$R_{{\mathrm{NH}}_3}$ and EE values reaching 5.7 µmol.min⁻¹.g_cat⁻¹ and 4.5 g-NH₃ [kWh.g_cat⁻¹]⁻¹, respectively. Characterization of the catalysts by powder X-Ray Diffraction (XRD) revealed the formation of La(OH)₃ from La₂O₃ in the presence of electric field, and an altered reaction mechanism was observed. The temperature-dependent study showed an increase in NH₃ production at 150 °C and 200 °C with an apparent activation energy of 30 kJ.mol⁻¹.