Iron Loading Effects in Fe/SSZ-13 NH3-SCR Catalysts: Nature of the Fe Ions and Structure–Function Relationships

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• 作者：Feng Gao ; Yang Zheng ; Ravi K. Kukkadapu ; Yilin Wang ; Eric D. Walter ; Birgit Schwenzer ; János Szanyi ; Charles H. F. Peden
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：May 6, 2016
• 年：2016
• 卷：6
• 期：5
• 页码：2939-2954
• 全文大小：824K
• 年卷期：0
• ISSN：2155-5435

文摘

Using a traditional aqueous solution ion exchange method under a protecting atmosphere of N₂, a series of Fe/SSZ-13 catalysts with various Fe loadings were synthesized. UV–vis, EPR, and Mössbauer spectroscopic methods, coupled with temperature-programmed reduction and desorption techniques, were used to probe the nature of the Fe sites. The major Fe species are extraframework Fe(III) species: [Fe(OH)₂]⁺ (monomeric) and [HO–Fe–O–Fe–OH]²⁺ (dimeric). Larger oligomers with unknown nuclearity, poorly crystallized Fe oxide particles, together with isolated Fe²⁺ ions, are minor Fe-containing moieties. Reaction rate and Fe loading correlations, and temperature and Fe loading effects on SCR selectivities, suggest that isolated Fe³⁺ ions are the active sites for low-temperature standard SCR, and dimeric sites provide the majority of reactivity at higher temperatures. For NO oxidation, dimeric sites are the active centers. NH₃ oxidation, on the other hand, is catalyzed by sites with higher nuclearity.