NO2and NO Adsorption Properties of KOH-Treated γ-Alumina

Abstract

A method to control nitrogen oxide (NOx) emissions from combustion sources by adsorption of NO2 and NO on γ-alumina before and after KOH treatments has been evaluated. Compared to previously studied sorbents consisting of magnesium-oxide-coated vermiculite, untreated γ-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 γ-alumina with KOH by impregnation or precipitation improves the adsorptive properties of γ-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 γ-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 γ-alumina exposed to NOx. A 40% loss of BET surface area occurs due to KOH precipitation on γ-alumnia 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 γ-alumina. Washing the γ-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.