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.
Highlights
NOx emission from diesel engines causes severe environmental issues such as acid rain, photochemical smog, and haze.[1]
Selective catalytic reduction (SCR) of NOx is the commercial technology utilized for NOx elimination in heavy-duty diesel engine vehicles.[2]
It was proposed that the valence state of silver species affected the performance roeflaAtged/Atlo2Oth3einfoHrm2-aCti3oHn6-oSfCiRnecrtonsutarifnacinegfomrmoisattuer.1e4,1w5hich was Sulfur poisoning is another challenge for HC-SCR catalysts, the amount of sulfur dioxide in diesel engine exhausts has gradually decreased.[16−21] Ag/Al2O3 catalysts show moderate sulfur resistance in HC-SCR, related to the reaction conditions.[22−25] In general, SO2 can react with the active sites to produce stable sulfates, suppressing NOx reduction.[22−24] Meunier et al.[23] proposed that these sulfate species resulted in permanent deactivation of 1.2 wt % Ag/Al2O3 in C3H6-SCR
Summary
NOx emission from diesel engines causes severe environmental issues such as acid rain, photochemical smog, and haze.[1]. Since diesel engine exhausts contain a lot of moisture, SCR catalysts must have excellent water resistance. Similar suppression was found on 5 wt % Ag/Al2O3 in H2-C3H8-SCR.[13] Besides, it was proposed that the valence state of silver species affected the performance roeflaAtged/Atlo2Oth3einfoHrm2-aCti3oHn6-oSfCiRnecrtonsutarifnacinegfomrmoisattuer.1e4,,1w5hich was Sulfur poisoning is another challenge for HC-SCR catalysts, the amount of sulfur dioxide in diesel engine exhausts has gradually decreased.[16−21] Ag/Al2O3 catalysts show moderate sulfur resistance in HC-SCR, related to the reaction conditions.[22−25] In general, SO2 can react with the active sites to produce stable sulfates, suppressing NOx reduction.[22−24] Meunier et al.[23] proposed that these sulfate species resulted in permanent deactivation of 1.2 wt % Ag/Al2O3 in C3H6-SCR. It was reported that the nature of the reductant affected the performance of Ag/Al2O3 in HC-SCR containing SO2.24 More recently, it was proposed that the sulfur resistance of Ag/Al2O3 is affected by the mobility of sulfate species, which is closely related to the state of silver species.[27]
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