Nanoarray-Based Monolithic Adsorbers for SO 2 Removal

Abstract

Nanoarray-based monolithic catalysts have been developed for various applications, including CO oxidation, hydrocarbon combustion, lean NO x trapping, and low-pressure CO 2 hydrogenation. In this work, SO 2 adsorption properties have been explored and evaluated on the cordierite honeycomb monoliths grown with zinc oxide nanoarray (ZnO), zinc oxide nanoarray washcoated by BaCO 3 nanoparticles (ZnO/BaCO 3 ), and manganese oxide nanowire array with cryptomelane structure (MnO x ) at a temperature range from 50 to 425 °C. All samples show temperature-dependent SO 2 adsorption behaviors. The adsorption results reveal the performance order: MnO x > ZnO/BaCO 3 > ZnO, with ~ 90% SO 2 adsorbed in MnO x at 425 °C. Washcoated BaCO 3 contributes to the improvement of SO 2 adsorption in ZnO nanoarray, and the best performance displayed in MnO x may be attributed to their high specific surface area. After regeneration, nanoarrays all exhibit good thermal stability during test-regeneration cycles. No additional phase is formed in regenerated ZnO nanoarrays (ZnO-R), while BaCO 3 is converted to BaSO 4 in the regenerated ZnO/BaCO 3 nanoarrays (ZnO/BaCO 3 -R), and the sulfur species (possibly MnSO 4 ) and Mn 2 O 3 are found in regenerated MnO x nanoarrays (MnO x -R). It is noted that a small amount of sulfur species (possibly MnSO 4 ) may promote the SO 2 adsorption of MnO x -R at a lower temperature, while the formed Mn 2 O 3 contributes to the deactivation of MnO x -R.