Abstract
Herein, Cu-modified SAPO-34 catalysts with various copper loadings are synthesized via a pH-controlled ion-exchange method. Cu exists predominantly as isolated cations at lower loadings, located at octahedrally coordinated sites in the ellipsoidal cavity of SAPO-34 zeolites, while CuO is gradually generated on the external surface at higher loadings. Our results reveal that the isolated Cu cations are the active sites for C₃H₆-SCR. The presence of CuO species enhances the C₃H₆ activation ability of the catalysts, which thus, improves the C₃H₆-SCR performance at medium and low temperatures (below 400 °C). At high temperatures, however, the formation of CuO accelerates the nonselective oxidation of C₃H₆ and causes activity decline. These findings suggest that the active temperature window for hydrocarbons-selective catalytic reduction (HC-SCR) reactions over Cu/SAPO-34 catalysts can be tailored by tuning the proportion of various copper species to fit the need in real applications, which provide new insights into understanding and designing highly efficient Cu-based zeolite catalysts.
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