THE SORPTION AND REDUCTION OF NITROGEN-OXIDES BY 12-TUNGSTOPHOSPHORICACID AND ITS AMMONIUM SALT

Nitrogen dioxide is removed from the gas phase by 12-tungstophosphoric (HPW), 12-tungstosilicic and 12-molybdophosphoric acids, with the two solid acids containing tungsten sorbing significantly larger quantiti es of NO2 than that containing molybdenum, indicating the dependence o n acidic strength. NO2 interacts with the water contained on and in HP W to form HNO3 which desorbs. On depletion of the water additional NO2 remains held on HPW as HNO2+. In contrast the ammonium salt of HPW re duces NO2 to N-2, NO and N2O at an optimal temperature of 175 degrees C for the reduction to N-2. The interaction process occurs between NO2 and the reductant NH3 while it is bound as NH4+ on the solid. Thus NH 3 is not lost to the gas phase during the reduction process, and ammon ia slip is effectively eliminated. The ammonium salt can be regenerate d by exposure of HPW to gaseous NH3 or by precipitation from aqueous s olution. (C) 1998 Elsevier Science B.V. All rights reserved.