Investigation of Water and Sulfur Tolerance of Precipitable Silver Compound Ag/Al2O3Catalysts in H2-Assisted C3H6-SCR of NO x

Abstract

Ag/Al2O3 catalysts containing different precipitable silver compounds (AgCl, Ag2SO4, and Ag3PO4) were synthesized and investigated for NOx reduction in H2-assisted C3H6-selective catalytic reduction (SCR). The samples were systematically characterized by N2 adsorption, X-ray diffraction (XRD), UV-Vis, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM). N2 adsorption revealed that the introduction of anions (Cl-, SO42-, and PO43-) did not significantly affect the surface and structural properties of the Al2O3 support. However, XRD patterns and HR-TEM images indicated that the addition of Cl- anions caused the agglomeration of silver species to form large AgCl particles on the AgCl/Al2O3 catalysts. In contrast, the silver species dispersed well on Ag2SO4/Al2O3 and Ag3PO4/Al2O3 catalysts. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed that partial oxidation of C3H6 on Ag2SO4/Al2O3 produced large amounts of reactive enolic species, while it tended to yield inert formate on AgCl/Al2O3. As a result, Ag2SO4/Al2O3 catalysts, especially 3% Ag2SO4/Al2O3, exhibited superior water and sulfur tolerance in H2-assisted C3H6-SCR.