A method to control nitrogen oxide (NO x ) emissions from combustion sources by adsorption of NO 2 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 NO x indicate that potassium influences the NO x -sorption process. Subsequent treatment of γ-alumina with KOH by impregnation or precipitation improves the adsorptive properties of γ-alumina toward both NO 2 and NO, with the precipitated samples performing better than impregnated samples. This research confirms previous findings that sorption of 3 mol of NO 2 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 NO 2 adsorbed. Formation of nitrate and nitrite species is observed by XPS analysis of KOH-precipitated γ-alumina exposed to NO x . 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 NO x . 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 NO x 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.
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Lee et al. (1998) studied this question.
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