(6az) The Synergistic Effect of Copper and Niobium Species on a Novel Cu/Nb-Ti Mixed Oxide Catalyst for the Selective Catalytic Reduction of NOx with NH3

Research Interests: A series of titanium-niobium oxide as the catalyst support was first synthesized by co-precipitation and then Cu/Nb-Ti ternary oxide catalyst was prepared through wetness impregnation. The optimal proportion was explored.And 0.8%Cu/Ti₂NbO_x exhibited the best catalytic activity with NO_x conversion and N₂ selectivity maintaining upon 90% and 97% respectively in the temperature range of 250^oC-425^oC under a gas hourly space velocity (GHSV) of 177,000h^-1. 0.8%Cu/Ti₂NbO_x showed well activity while traditional commercial VWTi catalyst deactivated after 2%K₂O doping. Water vapor or SO₂ would not pose any negative effect on the SCR activity while the catalytic performance showed a slightly reversible inhibition with water vapor and SO₂ existing in the simulated gas stream simultaneously. Also, 0.8%Cu/Ti₂NbO_x had an excellent hydrothermal stability after the process of hydrothermal aging with 10%H₂O, 5%O₂ and N₂ as balance for 7h at 800^oC.The activity characterization indicated 0.8%Cu/Ti₂NbO_x was a promising candidate for the NH₃-SCR catalyst in the future practical application.

Teaching Interests: An array of analytical techniques (HRTEM, XRD, LRS, XPS, EPR, in-situ DRIFTS etc.) were employed to elucidate the correlations among the “performance – structure – property” and the reaction mechanism over 0.8%Cu/Ti₂NbO_x catalyst. The introduction of niobium oxide increased the surface area of TiO₂ and decreased the crystallite size, promoting the high dispersion of copper species. Meanwhile, the total acidity and the amount of surface active oxygen over the catalyst were increased by the addition of niobium oxide. Copper species mainly existing in the state of isolated Cu²⁺ and non-isolated Cu⁺ enhanced the redox capability of the catalyst and the highest ratio of isolated Cu²⁺/copper species resulted in an excellent catalytic performance of 0.8%Cu/Ti₂NbO_x. The promotional synergistic effect of copper and niobium in 0.8%Cu/Ti₂NbO_x catalyst gave rise to a better NH₃-SCR performance. Furthermore, the reaction pathway over 0.8%Cu/Ti₂NbO_x catalyst followed both Eley-Rideal mechanism and Langmuir-Hinshelwood mechanism at 225^oC. Both coordinated NH₃ and ionic NH⁴⁺ were active intermediates and monodentate nitrates, bidentate nitrates and bridging nitrates were involved in the reaction over 0.8%Cu/Ti₂NbO_x catalyst at the reaction temperature of 225^oC.

https://doi.org/10.1016/j.apcatb.2017.08.021