NO2 and NO adsorption properties of KOH-treated γ-alumina

A method to control nitrogen oxide (NOx) emissions from combustion sources by adsorption of NO2 and NO on gamma-alumina before and after KOH treatments has been evaluated. Compared to previously studied sorbents consisting of magnesium-oxide-coated vermiculite, untreated gamma-alumina exhibits a 6-fold increase in activity in tubular flow system tests. XPS analyses of the adsorbent surfaces before and after exposure to NOx indicate that potassium influences the NOx-sorption process. Subsequent treatment of gamma-alumina with KOH by impregnation or precipitation improves the adsorptive properties of gamma-alumina toward both NO2 and NO,with the precipitated samples performing better than impregnated samples. This research confirms previous findings that sorption of 3 mol of NO2 on gamma-alumina results in the catalytic formation of 1 mol of NO. However, treatment with KOH delays and reduces the formation of NO while increasing 5-fold the amount of NO2 adsorbed. Formation of nitrate and nitrite species is observed by XPS analysis of KOH-precipitated gamma-alumina exposed to NOx. A 40% loss of BET surface area occurs due to KOH precipitation on gamma-alumina followed by a further 56% loss in surface area after saturation with NOx. The addition of water vapor (3 vol %) to the feed gas stream significantly enhances the adsorption properties of the KOH-treated gamma-alumina. Washing the gamma-alumina pellets exposed to NOx with water essentially removes all of the potassium nitrates and nitrites formed. This harmless solution can be disposed of safely or used as fertilizer, and the pellets can be regenerated.