Nanoarray-Based Monolithic Adsorbers for SO2 Removal

Abstract

Nanoarray-based monolithic catalysts have been developed for various applications, including CO oxidation, hydrocarbon combustion, lean NOx trapping, and low-pressure CO2 hydrogenation. In this work, SO2 adsorption properties have been explored and evaluated on the cordierite honeycomb monoliths grown with zinc oxide nanoarray (ZnO), zinc oxide nanoarray washcoated by BaCO3 nanoparticles (ZnO/BaCO3), and manganese oxide nanowire array with cryptomelane structure (MnOx) at a temperature range from 50 to 425 °C. All samples show temperature-dependent SO2 adsorption behaviors. The adsorption results reveal the performance order: MnOx > ZnO/BaCO3 > ZnO, with ~ 90% SO2 adsorbed in MnOx at 425 °C. Washcoated BaCO3 contributes to the improvement of SO2 adsorption in ZnO nanoarray, and the best performance displayed in MnOx 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 BaCO3 is converted to BaSO4 in the regenerated ZnO/BaCO3 nanoarrays (ZnO/BaCO3-R), and the sulfur species (possibly MnSO4) and Mn2O3 are found in regenerated MnOx nanoarrays (MnOx-R). It is noted that a small amount of sulfur species (possibly MnSO4) may promote the SO2 adsorption of MnOx-R at a lower temperature, while the formed Mn2O3 contributes to the deactivation of MnOx-R.