Molten nitrate/ceramic membranes of KNO₃/Al₂O₃ and KNO₃/La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) were designed and successfully operated for the selective permeation of nitrogen oxides. With the presence of oxygen on the feed side of the membrane, the KNO₃/Al₂O₃ membrane showed no measurable oxygen permeation while the KNO₃/LSCF membrane exhibited nitrogen dioxide and oxygen co-permeation. For the KNO₃/LSCF membrane, a permeance of up to 6.9 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ was achieved while the nitrogen dioxide to oxygen permeate ratio appeared to be approximately constant with a value of around unity.