Effect of Preparation Method on Cu Active Sites and the Reaction Pathway in NO Reduction by NH₃ over Cu–SSZ-13

Abstract

To study the influence of the preparation method on Cu active sites and the reaction pathway in NO reduction by NH₃ over Cu–SSZ-13, three kinds of catalysts (Cu ion-exchanged SSZ-13¹, one-pot synthesis Cu–SSZ-13², and Ce_0.017–Fe_0.017/Cu–SSZ-13 [Ce and Fe ion exchange on the basis of Cu–SSZ-13²]) were prepared. In situ diffuse reflectance infrared Fourier transform spectroscopy and H₂ temperature program reduction were used to study the differences in the reaction pathways and Cu active sites over the three kinds of catalysts. Density functional theory was employed to study the effect of active sites on the reaction pathway. In situ DRIFTS showed that the reaction pathway on Cu–SSZ-13¹ during NO oxidation was different from that on Cu–SSZ-13² and Ce_0.017–Fe_0.017/Cu–SSZ-13. The difference was that intermediate NO₂ was involved in the selective catalytic reduction reaction on Cu–SSZ-13¹, whereas NO₂ was not found during the reaction process on Cu–SSZ-13² and Ce_0.017–Fe_0.017/Cu–SSZ-13. H₂–TPR studies revealed that the three catalysts had different Cu active sites, which were located in the six-membered ring, eight-membered ring, and CHA cage. On the basis of DFT studies, NO and O₂ were more conducive to form nitrate when the Cu species was on the six- and eight-membered rings; by contrast, NO and O₂ were more conducive to form NO₂ in the cage. These results showed that different preparation methods led to various Cu active sites, and varying Cu active sites could lead to different NO oxidation processes.

Keywords

Selective catalytic reduction / NO _x removal / SSZ-13 / In situ DRIFTS / Active site / DFT

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