Development of new sorbent material for reversible removal of air pollutants using catalytic reactions

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It was earnestly desired to develop the effective removal methods or harmful compounds such as NO_X and HCl in the exhaust gases as pollutants. However, it was very difficult to convert these pollutants to harmless compounds on catalysts, because some components in the exhaust gases poisoned the catalyst. In this project, we tried to develop the solid oxide sorbents on which these pollutants were absorbed, concentrated, and reversibly released. We prepared ZrO_2-based sorbents such as Pt-ZrO_2/Al_2O_3 and MnO_y-ZrO_2, On these sorbents NO was catalytically oxidized to nitrate ions, and they moved to the Zr sites. The effect of calcinations temperature and preparation procedures on their NO_X removal capacity was investigated. When H_2PtCl_6 was used as starting materials, high temperature calcination was necessary to remove residual chlorine on the surface of the sorbent. The residual chlorine was not removed by at low temperature calcinations. We found out that when Cl-free compound was used as starting materials, the removal capacity was enhanced by high dispersion of Pt. The ZrO_2-Al_2O_3 support prepared by the coprecipitation method was impregnated with Pt(NO_2)_2(NH_3)_2 solution, and this catalyst showed highest activity in this project. Although ZrO_2-Al_2O_3 did not store NO, it stored NO_2 obtained by oxidation of NO.We found out that catalysts played an important role in store and release reactions at high velocity. While NO removal reaction needed relatively a larger amount of Pt, NO_2 removal reaction needed a trace amount of relatively inactive compounds such as Co and Mn, which enhanced both store and release reactions.