Electrochemical processes using solid gas-impervious membranes are disclosed for gas cleanup by (A) providing an electrochemical cell comprising first and second zones separated by a solid gas-impervious membrane comprising a mixed metal oxide material of a perovskite structure having electron conductivity and oxygen ion conductivity, (B) passing a gas containing N2O, NO, NO2, SO2, SO3, or a mixture thereof, in contact with the membrane in the first zone, and (C) passing a gas capable of reacting with oxygen in contact with the membrane in the second zone. More particularly, the mixed metal oxide material of a perovskite structure comprises a combination of elements selected from the group consisting of lanthanides, alkaline earth metals, Y, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, and Nb, oxides thereof, and mixtures of these metals and metal oxides. Advantageously a catalyst is present in the first zone.