Solid Sorbent Control of Nitrogen Oxides (NOx)

Solid materials have demonstrated applicable control of combustion-source NOx. A support material of (gamma)-alumina can provide improved NOx sorption in comparison to a previously applied sorbent, magnesia-coated vermiculite. NOx sorption of treated (gamma)-alumina correlates with the ionization potential of the group-1 element. General mechanisms of NOx sorption have been developed for untreated, K2CO3-treated and KOH-treated (gamma)-alumina. Sorption of NO appears to increase formation of nitrine. Untreated (gamma)-alumina formed little nitrite. For the treated (gamma)-alumina, the ratio of nitrite-nitrate formed relates to the ratio of NO-to-NO2 sorbed. Additional NO2 exposure converts nitrite into nitrate and NO. This nitrite-to-nitrate conversion correlates with the thermal stability of subsurface species. In addition, thermal-decomposition tests indicated similarities of NOx-exposed sorbents to nitrite and nitrate salts. The proposed mechanisms suggest that formed nitrite stability is crucial to improving NOx sorption. Effects of additional gases (O2, SO2, CO2, or water vapor) to NO and NO2 sorption at 25 and 250 deg C by untreated, K2CO3-treated and KOH-treated (gamma)-alumina were evaluated. Only SO2 and water vapor were observed to affect NOx sorption.