Intimate contact of enolic species with silver sites benefits the SCR of NOx by ethanol over Ag/Al2O3

• Published in: Journal of catalysis 2012-09, Vol.293, p.13-26
• Main Authors: Yan, Yong, Yu, Yunbo, He, Hong, Zhao, Jiaojiao
• Format: Article
• Language: English
• Subjects: Acetate; Adsorption; Ag/Al2O3; Catalysis; Chemistry; Enolic species; Ethanol; Exact sciences and technology; General and physical chemistry; Isocyanate; Nitric oxide; Oxidation; Selective catalytic reduction of NOx; Spectrum analysis; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2012.05.021

The enolic species derived from the partial oxidation of ethanol over Ag/Al2O3 prefer to adsorb on or close to silver sites, which exhibits an intimate contact with the active phase. Such adsorption behavior of enolic species benefits the formation of isocyanate species, which finally contributes the high activity of Ag/Al2O3 for the selective catalytic reduction of NOx by ethanol. [Display omitted] ► Oxidized Ag species are responsible for the NOx reduction by ethanol on Ag/Al2O3. ► Enolic species and acetate formed during partial oxidation of ethanol on Ag/Al2O3. ► Surface enolic species prefer to adsorb on or close to Ag sites. ► Acetate is prone to adsorb on Al sites. ► The proximity of enolates to Ag is the key to NCO formation and NOx reduction. Alumina-supported silver (Ag/Al2O3) catalysts with different silver loadings were investigated for the selective catalytic reduction of NOx by ethanol. The catalytic role of silver in the formation of enolic species was studied by ultraviolet–visible spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy combined with mass spectrometry, density functional theory calculations, and kinetic measurements. It was found that the enolic species originating from the partial oxidation of ethanol over Ag/Al2O3 prefer to adsorb on or close to silver sites, in intimate contact with the active phase. This adsorption behavior of this enolic species contributes to its high activity for the formation of isocyanate species (NCO) and the final product N2 during the NOx reduction by ethanol over Ag/Al2O3. Surface acetate also formed during this process, while only interacting with Al sites, resulting in a lower activity for NCO formation. Meanwhile, the mechanism of the NOx reduction by ethanol was discussed.