Nanoarray-Based Monolithic Adsorbers for SO₂ Removal

Nanoarray-based monolithic catalysts have been developed for various applications, including CO oxidation, hydrocarbon combustion, lean NO_x 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 (MnO_x) at a temperature range from 50 to 425 °C. All samples show temperature-dependent SO₂ adsorption behaviors. The adsorption results reveal the performance order: MnO_x > ZnO/BaCO₃ > ZnO, with ~ 90% SO₂ adsorbed in MnO_x at 425 °C. Washcoated BaCO₃ contributes to the improvement of SO₂ 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 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 MnO_x nanoarrays (MnO_x-R). It is noted that a small amount of sulfur species (possibly MnSO₄) may promote the SO₂ adsorption of MnO_x-R at a lower temperature, while the formed Mn₂O₃ contributes to the deactivation of MnO_x-R.