Establishment of surface/bulk-like species functionalization by controlling the sulfation temperature of Sb/V/Ce/Ti for NH ₃ -SCR

Investigation of cerium sulfate species on sulfated SbVCT (Sb/V/Ce/Ti) catalysts at various temperatures was carried out by diffused-reflectance infrared Fourier-transform spectroscopy (DRIFTs) analysis. The catalyst sulfated at a high temperature, SbVCT (500s-1) (i.e., sulfated at 500 °C), exhibited higher NOx removal performance at low temperatures than the SbVCT (fresh) and VWTi catalysts. The in-situ DRIFTs results showed that the ionic character of SbVCT (500s-1) increased significantly, whereas SbVCT (250s-1) only had covalent character. For SbVCT (250s-1), a small amount of surface cerium sulfate species was formed. With increasing sulfation temperature, more cerium sulfate species formed as a bulk-like species, and its rate of formation increased. Bulk-like cerium sulfate species formed at high temperatures do not change upon exposure to low temperatures. However, surface cerium sulfate species formed at low temperatures underwent phase change to bulk-like species upon exposure to high temperatures. Catalysts containing bulk-like cerium sulfate species exhibit high SCR performance at low temperatures. Therefore, the SCR performance improved when the SbVCT (250s-1) was exposed to high temperatures. A related model has been proposed to understand how the interactions of sulfate species of SbVCT are affected by sulfation temperature. Furthermore, the SO ₂ resistance of SbVCT was superior to that of the VWTi catalyst because it delayed the adsorption of SO ₂ onto the catalytic surface. Through functionalization of cerium sulfate species, SbVCT can exhibit improved low-temperature activity and durability.