Development of zirconia-based oxide sorbents for removal of NO and NO2

Zirconia-based oxide sorbents for NOx has been investigated to clarify the role of additives. Addition of yttria to Mn–Zr oxide improved the sorption capacity due to enhanced basicity and larger surface area. A small amount of transition metal oxide as additives was effective in promoting the sorption–desorption capability. A small addition of Mn or Co to ZrO2 was effective in achieving reversible sorption and desorption of NOx due to their activity as a reduction–oxidation catalyst. These oxides were active for the oxidation of NO to nitrate ions via NO2 in an oxidizing atmosphere and reduction of nitrate ions in the presence of a gaseous reductant. The NOx sorptive capacities of Mn-containing sorbents were significantly deteriorated in dilute SO2. The NOx sorption capacity of 0.5 wt.% Co/ZrO2 was lowered only slightly in the initial stage of NO2 sorption with dilute SO2.