Ammonia synthesis and by-product formation from H₂O, H₂ and N₂ by dielectric barrier discharge combined with an Ru/Al₂O₃ catalyst

NH₃ synthesis from H₂O + N₂, H₂ + N₂ or H₂O + H₂ + N₂ by dielectric barrier discharge combined with an Ru/Al₂O₃ catalyst is studied at atmospheric pressure and room temperature. Additionally, the effects of reaction gas composition, energy density, and discharge frequency on NH₃ yield and by-product formation are investigated. The results show that NH₃ can be formed from reaction gases consisting of H₂O and N₂. The NH₃ yield of the reaction gas containing H₂ is much higher than that of the reaction gas consisting of H₂O and N₂. The presence of H₂O has a promotion effect on NH₃ synthesis from H₂ and N₂, especially for reaction gases with an H₂ content less than 10%. The NH₃ yield first increases and then decreases with an increase in the energy density. The maximum yield of 680 mg kW⁻¹ h⁻¹ occurs at the energy density of 1400 J L⁻¹ and in the reaction gas of 0.14% H₂O, 40% H₂ and N₂. The discharge frequency has a great effect on the NH₃ yield, and maximum NH₃ yield is obtained at the frequency of 13 kHz. Besides NH₃, some by-products, such as N₂O and NO₂, are also formed with reaction gases containing H₂O. However, their formation can be suppressed in the presence of H₂, which is attributed to the reduction effect of H₂ on the by-products.