The influence of chemical poisoning, hydrothermal aging and their co-effects on Cu-SAPO-34 catalyst for NOx reduction by NH3-SCR

Abstract

To investigate the effect of alkali (K and Na) and alkaline earth (Ca and Mg) metal poisoning and hydrothermal aging on Cu-SAPO-34 catalyst; a series of samples containing various metals (Mg, Ca, Na and K) loadings were prepared by an impregnation method, and the changes of catalytic properties were evaluated before and after hydrothermal aging by various characterization techniques. The results indicated that the surface area, the isolated Cu2+ ions and the acidity of Cu-SAPO-34 catalyst were well-maintained after low alkali and alkaline earth metal contents (0.50 mmol/gcat) incorporation. The results showed that at high content (1.50 mmol/gcat), the great decrease of SCR performance was explained by the destruction of the zeolite structure, the decrease in acidity and the transformation of Cu2+ ions to CuO detected by XRD, NH3-TPD and H2-TPR techniques, respectively. The NH3-SCR performance of the fresh and aged samples was similar after high-temperature (650 °C) hydrothermal aging treatment for 12 h. A slight increase of activity was observed when the samples were hydrothermal aging at 700 and 750 °C for 12 h due to the change of Cu species distribution. The NH3-TPD results show that the acidity was not affected by hydrothermal aging treatment. During hydrothermal aging process, CuO species first precipitated on the external surface and then dispersed as isolated Cu2+ ions over Cu-SAPO-34. The Cu-SAPO-34 could withstand the co-effect of chemical poisoning (K, Na and Ca) and hydrothermal aging at 750 °C at the same times. In summary, our results indicated that the pore blocking, disruption of the zeolite framework, reduction of acid sites and active sites were the reasons for the chemical the deactivation of Cu-SAPO-34 catalyst after the introduction of metals.