Improved hydrothermal stability of Cu-SAPO-18 by Sm modification in the selective catalytic reduction of NOx with NH3

Abstract

The Cu-SAPO-18 catalyst is efficient for the selective reduction of NOx with NH3 reaction. Nonetheless, enhancement of the hydrothermal stability of the Cu-SAPO-18 catalyst is needed to satisfy the stringent emission regulations. Sm with partially occupied 4 f orbitals and unoccupied 5d orbitals exhibits excellent physical and chemical properties and is often used as a catalyst promoter in catalytic reactions. In this study, we introduced Sm to Cu-SAPO-18 by a hydrothermal method, and when the added amount of Sm was 0.78 wt%, there was a significant improvement in hydrothermal stability. After Sm introduction, there was a decrease in Si(4Si, 0Al) amount and in unstable Cu(OH)+-Z concentration, thus inhibiting the formation of CuO species during hydrothermal aging. Simultaneously, the Sm replaced the hydrogens of a certain amount of Si–OH–Al bonds, stabilizing the Si–O–Al bonds and alleviating the Cu-SAPO-18 dealumination. Besides, after hydrothermal aging, there was an increase of isolated Cu2+ content in Sm0.78/Cu-SAPO-18, consequently promoting the adsorption of NH3 and NOx species and enhancing the Langmuir–Hinshelwood reaction rate.