Investigating the role of H4SiW12O40 in the acidity, oxidability and activity of H4SiW12O40-Fe2O3 catalysts for the selective catalytic reduction of NO with NH3

Abstract

A series of H4SiW12O40-modified Fe2O3 catalysts were synthesized using the precipitation method. Over 80% NOx conversion was obtained in the temperature region of 250–450 °C for the catalysts with the H4SiW12O40 content of 5% and 10%. The relationship between the physicochemical properties and performances of the series catalysts was established. Abundant acid sites were introduced with doping H4SiW12O40, which promoted the adsorption of reductant NH3 on the catalysts at high-temperature regions. Moreover, adding H4SiW12O40 lowered the amount and reducibility of catalyst surface reactive oxygen species, which inhibited the oxidation of NH3 to NOx at higher temperatures to some extent. Thus, most ammonia species were prone to participating in the reaction with NOx instead of being directly oxidized to NOx in the higher temperature region over the H4SiW12O40-decorated catalysts. And it could be concluded that the balance of the acid and redox properties constituted the main reason for the superior activity of the high H4SiW12O40 content catalysts. Additionally, SO2 exerted a slight and reversible inhibition effect on the catalyst activity at 300 °C, suggesting that HSiW-modified Fe2O3 oxide might be a promising catalyst in practical applications.