Investigation of low-temperature hydrothermal stability of Cu-SAPO-34 for selective catalytic reduction of NOx with NH3

Abstract

The low-temperature hydrothermal stabilities of Cu-SAPO-34 samples with various Si contents and Cu loadings were systematically investigated. The NH3 oxidation activities and NH3-selective catalytic reduction (SCR) activities (mainly the low-temperature activities) of all the Cu-SAPO-34 catalysts declined after low-temperature steam treatment (LTST). These results show that the texture and acid density of Cu-SAPO-34 can be better preserved by increasing the Cu loading, although the hydrolysis of Si–O–Al bonds is inevitable. The stability of Cu ions and the stability of the SAPO framework were positively correlated at relatively low Cu loadings. However, a high Cu loading (e.g., 3.67 wt%) resulted in a significant decrease in the number of isolated Cu ions. Aggregation of CuO particles also occurred during the LTST, which accounts for the decreasing NH3 oxidation activities of the catalysts. Among the catalysts, Cu-SAPO-34 with a high Si content and medium Cu content (1.37 wt%) showed the lowest decrease in NH3-SCR because its Cu2+ content was well retained and its acid density was well preserved.