Establishment of surface/bulk-like species functionalization by controlling the sulfation temperature of Sb/V/Ce/Ti for NH3-SCR

Abstract

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 degrees 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 SO2 resistance of SbVCT was superior to that of the VWTi catalyst because it delayed the adsorption of SO2 onto the catalytic surface. Through functionalization of cerium sulfate species, SbVCT can exhibit improved low-temperature activity and durability.