Hydrothermal conversion of FAU zeolites: Optimization of AEI zeolite synthesis and evaluation of low-temperature CO oxidation activity
Zeolite-based catalysts are extensively investigated for industrial applications due to their unique pore structure, remarkable thermal/hydrothermal stability, and abundant acid sites. However, the inherent lack of active sites for oxygen activation in non-reducible supports leads to suboptimal low-temperature oxidation activity. This study synthesized SSZ-39 (AEI-type) zeolite via interzeolite transformation from Y (FAU-type) zeolite, exploring the effects of gel composition on its structural properties and the influence of different cerium precursor salts on the CO oxidation performance of platinum-loaded zeolite catalysts. The results show that introducing seed crystals can replace 40 % of the organic structure-directing agent, leading to the synthesis of pure SSZ-39 zeolite with a specific surface area of 588 m 2 /g, where aluminum species are solely present as framework aluminum. The Pt-8Ce(ca)/SSZ-39 catalyst, prepared using cerium acetate as the precursor, demonstrates excellent low-temperature activity and stability, achieving 100 % CO conversion at 150 °C and maintaining it for over 100 h. After hydrothermal aging at 750 °C, the conversion temperature increased by only 20 °C, with the outstanding hydrothermal stability attributed to the stable framework structure of SSZ-39 zeolite. The highly dispersed Pt-CeO 2 interface increases surface-active oxygen species, which induce the transition from the L-H to the MvK reaction mechanism. This reduces competitive adsorption between O 2 and CO, and the oxygen vacancies formed during the reaction serve as additional O 2 activation sites, addressing the low-temperature CO oxidation issue in non-reducible support zeolite-based catalysts.
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