Enhanced NOx Catalytic Reduction by NH3 over Polymeric Sulfur Species in CeO2 via Tailoring Ce-O Bonds.

Abstract

Sulfate-modified CeO2 is one of the effective routes to improving the performance of NH3-SCR; however, tailoring sulfur species and their effect on the Ce-O bond and NOx removal remains challenging. Herein, we rationally designed an excellent sulfate-modified ceria-based NH3-SCR catalyst by tuning the sulfate species to tailor chemical bonds in CeO2. NOx conversion was dramatically enhanced from 40% (conventional sulfuric acid impregnated CeO2-S catalyst) to 100% of the synthesized CeO2-TDC at 250 °C. By using Ce L3-edge XANES with various characterizations and density functional theory calculations, it was found that, in addition to the sulfate species in CeO2-S and CeO2-TDC, the polymeric state sulfate was also observed in CeO2-TDC, which redistributed the electron density between Ce sulfate and reduced the Ce-O bond length. Moreover, the reaction processes of NH3 to NH4+/*NH2 and NO to monodentate nitrate were more facilitated on CeO2-TDC via the synergistic interactions of rich Lewis acidic Ce4+, Brønsted acidic S-OH, and enhanced redox, thus achieving the Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) pathways, whereas only the E-R mechanism was on the conventional CeO2-S. This work provides a novel strategy for designing highly efficient sulfate-modified NH3-SCR catalysts.