Unveiling a remarkable enhancement role by designing a confined structure Ho-TNTs@Mn catalyst for low-temperature NH₃-SCR reaction

Abstract

MnO_<i>x</i>-based catalysts are considered promising alternative catalysts for NH₃-SCR to remove NO_<i>x</i> at low temperature. However, their poor SO₂ or H₂O tolerance and unfavorable N₂ selectivity are still the main obstacles restraining their further practical application. Herein, we carefully confined the manganese oxide active species in Ho-modified titanium nanotubes to improve their SO₂ resistance and N₂ selectivity. Ho-TNTs@Mn exhibits excellent catalytic activity, strong SO₂ and H₂O tolerance and superior N₂ selectivity, and more than 80% NO conversion can be achieved in the range 80-300 °C with 100% N₂ selectivity. The characterization results verify that the pore confinement effect of Ho-TNTs for Mn increases the dispersion of Mn to promote the interfacial effect between Mn and Ho. The electron synergistic effect between Mn and Ho improves the electron transformation of Mn and Ho, which inhibits electron transfer between SO₂ and Mn to avoid poisoning from SO₂. We also find that the interaction between Ho and Mn induces electron migration to restrain the production of Mn⁴⁺, contributing to the suitable redox capacity to decrease the creation of byproducts, which serves as the motivation for high N₂ selectivity. <i>In situ</i> DRIFTs analysis clarifies that Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms co-exist in the NH₃-SCR reaction over Ho-TNTs@Mn, and the E-R reaction mechanism predominates We believe that Ho-TNTs@Mn with a well-designed nanotube structure will show preferable development and application prospects in the NH₃-SCR reaction.