Investigation of long-term anti-sulfur and deactivation mechanism of monolithic Mn-Fe-Ce/Al2O3 catalysts for NH3-SCR: Changes in physicochemical and adsorption properties
Owing to the different reaction properties and deactivation mechanisms caused by the structural discrepancy of monolithic catalysts, abundant scientific results of powder or granular NH 3 -SCR catalysts have still not sufficiently robustly applied in recent years. Furthermore, minimal research has been focused on monolithic catalysts. As a result, this work prepared monolithic Mn-Fe-Ce/Al 2 O 3 catalysts by active component impregnation (ACI-Mn-Fe-Ce/Al 2 O 3 ) and precursor impregnation methods (PI-Mn-Fe-Ce/Al 2 O 3 ) and investigates the long-term SO 2 and H 2 O resistance of the catalysts. Compared with the PI-Mn-Fe-Ce/Al 2 O 3 catalyst, the monolithic ACI-Mn-Fe-Ce/Al 2 O 3 catalyst showed better performance. The catalytic activity follows a bell-shaped curve with an optimal performance at a drug loading of 5 %. The ACI-Mn-Fe-Ce/Al 2 O 3 catalyst exhibits long-term resistance to SO 2 and H 2 O and can still convert more than 70 % NO x after 168 h of SO 2 and H 2 O resistance test. Characterization of the ACI-Mn-Fe-Ce/Al 2 O 3 catalysts before and after the reaction showed that the reducibility decreased after the reaction, and more Mn 4+ was transformed into Mn 2+ to weaken the catalytic activity. However, more Fe 2+ and Ce 3+ were generated during the reaction, increasing the number of oxygen vacancies, oxygen defects, and hydroxyl-like groups, all of which would contribute to a certain extent to counteract the passivation effect of SO 2 on the catalysts. In situ DRIFTs analysis shows that the formation of surface sulfates has a minimal effect on the adsorption of NO, but it does affect the adsorption of coordinated NH 3 on Lewis acid sites. This work elucidates the deactivation details of Mn-Fe-Ce/Al 2 O 3 catalysts from the perspective of physicochemical properties, which provides a reference for the development of better low-temperature SO 2 -resistance catalysts for industrial applications.
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