Effects of Synthesis Conditions on Rare Earth Doped Iron Oxide Catalyst for Selective Catalytic Reduction of NOx with NH3

ABSTRACT

A series of rare earth-doped Fe-based oxide catalysts were prepared by co-precipitation method as Selective Catalytic Reduction (SCR) catalysts. The effects of the various rare earth species, doping amount of Sm, calcination temperature and the kind of precipitant on the deNO_x activity of the catalysts were systematically investigated. The SO₂ resistance performance was tested on the optimal catalyst. The catalysts have been characterized by X-ray diffraction (XRD), The X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM) and Brunner Emmet Teller (BET). The results showed that the doping of Sm significantly improves the removal efficiency of Fe-based oxides. Sm_0.075Fe_0.925 catalyst showed the optimal deNO_x performance and excellent resistance to SO₂. At the optimal doping rate (0.075), the denitrification rate was close to 100% between 200 and 250°C. The calcination temperature has a significant effect on the catalyst. The order of catalytic activity for different calcination temperatures was 350°C ≈ 400°C > 450°C > 500°C. The Sm_0.075Fe_0.925 achieved 100% the de-NOx efficiencies at calcination temperatures of 350–400°C. It was also found that the deNO_x performance of the catalyst prepared by using NH₃·H₂O as the precipitating agent was better than the catalyst prepared by using (NH₃)₂CO₃ or NaOH as the precipitating agent. Normally a small amount of SO₂ would render the catalyst inactive, but the Sm_0.075Fe_0.925 catalyst was basically regenerated after 0.05% SO₂ removal in this resistance test.