In situ FTIR spectroscopy of highly dispersed FeOx catalysts for NO reduction: Role of Na promoter

• Na increases NO reduction by CO activity in FeOx/CeO2, up to 4X via NaFeEDTA synthesis.
• Stoichiometric synthesis (Fe:Na = 1:1) is preferred; excess Na did not improve activity.
• In situ FTIR spectroscopy identified unique NO adsorption (1460 cm−1) on NaFeEDTA/CeO2.
• NO intermediates are more reactive with Na present, i.e., faster consumption of FTIR bands.
• Na is a promoter with both structural (synthesis) and mechanistic (adsorption) roles.

The effect of Na on highly dispersed FeOx impregnated onto CeO2via the unique precursor Na/Fe-ethylenediaminetetraacetate (NaFeEDTA) was investigated by comparison to a series of well-defined catalysts synthesized by the traditional precursor Fe(NO3)3 both with and without Na addition. Catalysts were evaluated for steady-state NO reduction by CO and activities varied based on synthesis method and Fe:Na ratio. Na contributed a promoter effect when added at a stoichiometric ratio (Fe:Na = 1), providing an explanation for the higher activity of NaFeEDTA/CeO2 for NO reduction by CO. Activity decreased when excess Na was present in Fe(NO3)3 catalysts, but the stoichiometric promoter effect persisted up to ∼4.0 Fe/nm2. In situ Fourier transform infrared (FTIR) spectroscopy during NO adsorption revealed the presence of unique NO adsorption species (1460 cm−1) on the NaFeEDTA/CeO2, suggesting enhanced NO adsorption due to Na. At reaction temperature, FTIR bands of bulk nitrates on CeO2 were quantitatively shown to more rapidly undergo NO reduction catalytic transformations over NaFeEDTA/CeO2. These results increase understanding of mechanistic effects of Na on NO reduction over FeOx/CeO2 catalysts and serve to guide future design of oxide-based emission control catalysts that are free of Pt-group metals.

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