CeO_2−δ Nanoparticles Supported on SnNb₂O₆ Nanosheets for Selective Catalytic Reduction of NO_x with NH₃

Selective catalytic reduction with NH3 (NH3-SCR) is an effective technique for purifying flue gas by removing nitrogen oxides, and the catalyst plays a key role in this technology. For the purpose of developing novel, highly efficient, green, and vanadium-free catalysts, SnNb2O6 nanosheets were synthesized successfully by hydrothermal and solid reactions and confirmed by XRD and TEM. These nanosheets were first used as a support for CeO2−δ to prepare environmentally friendly Ce/SnNb2O6 catalysts for NH3-SCR. These Ce/SnNb2O6 catalysts had more than 90% NOx conversion and 98% N2 selectivity at 250–400 °C and a high space velocity of 120,000 mL/(g·h), which is higher than the per surface area performance of the previously reported Ce-based NH3-SCR catalysts. To explore the factors for this increased activity, NH3-TPD, H2-TPR, and XPS data were analyzed in detail. The results indicated that Ce/SnNb2O6 nanocatalysts have more acid and oxidative sites than Ce/SnO2 and Ce/Nb2O5. In addition, the surface of Ce/SnNb2O6 contained 39.4% Sn4+ ions, which synergize with Ce as additional redox sites. The effect of electron transfer between Sn and Ce at the interface promoted the formation of molecular oxygen and cycling of redox sites. Kinetic studies showed that Ce/SnNb2O6 had a low apparent activation energy of 38.0 kJ/mol, which reduced the difficulty of the reaction. DFT studies indicated that the adsorption energy of NH3 in SnNb2O6 was 429.7 kJ/mol, which is much higher than that of other common supports, meaning that NH3 is much easier to adsorb on SnNb2O6 nanosheets, therefore showing higher catalytic performance. Moreover, in situ DRIFTS analysis showed the changes in the dominant mechanisms: the L–H and E–R mechanism coexist at 300 °C, while most of the reactions follow the E–R mechanism at 400 °C. This study can provide new insights into the development of new Ce-based NH3-SCR catalysts to control NOx emissions from stationary sources.