Enhancement of performance and sulfur resistance of ceria-doped V/Sb/Ti by sulfation for selective catalytic reduction of NOx with ammonia

Abstract

A ceria-doped V/Sb/Ti catalyst prepared by sulfation was investigated for the selective catalytic reduction of NO_x by NH₃. The sulfation treatment was carried out at 250, 300, 400, and 500 °C. The properties of the catalysts were studied using physico-chemical analyses, including Brunauer–Emmett–Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS), H₂ temperature-programmed reduction (H₂-TPR), temperature programmed oxidation (TPO), NH₃ and NO temperature programmed desorption (TPD), transmission infrared spectra (IR), and thermal gravimetric analysis (TGA). The sulfated catalyst demonstrated increased activity due to the following reasons: (i) total acidity was increased by the formation of SO₄²⁻–NH₄⁺ on the surface of the catalyst; (ii) fast selective catalytic reduction (SCR) reaction was induced by the production of NO₂ through reaction of NO and O₂; (iii) the excellent SCR activity can be attributed to an enhancement in active oxygen species and chemisorption of NH₃. The SCR reaction over sulfated CeO₂ mainly enhanced the Eley–Rideal mechanism as compared to the V/Sb/Ce/Ti (Fresh). The sulfated catalyst demonstrated the best catalytic activity when sulfation was carried out at 500 °C for 1 h. At the same time, SO₂ resistance was also observed to be increased. On increasing the sulfation time, further increase in catalytic activity was not observed. In contrast, SO₂ resistance was decreased with prolonged sulfation. Sulfated ceria had positive effects on the catalytic activity; however, if formed at higher than appropriate levels, negative effects were observed on SO₂ deactivation. When considering the activity and SO₂ deactivation for the ceria-doped V/Sb/Ti catalyst, the optimal conditions for sulfation were 500 °C for 1 h.