Irregular influence of alkali metals on Cu-SAPO-34 catalyst for selective catalytic reduction of NOx with ammonia

SCR activity of Cu-SAPO-34 catalyst was reduced by alkali metal ions. The alkali metals ions (Li + , Na + and K + ) have shown irregular influences on Cu-SAPO-34. The order of poisoning strengths under 400 °C was found to be: Na +  > K +  > Li + , which is not consistent with the basicities of their corresponding metals. Experimental results and calculations showed that the alkali metal ions readily replace H + and Cu 2+ /Cu + ions. These exchanges result in the loss of Brønsted acid sites and migration of isolated Cu 2+ ions in Cu-SAPO-34, which decrease the NH 3 -SCR activity. Both the basicity and ion diameter will affect the exchanging behavior of an alkali ion. Na + and Li + ions will influence both H + and Cu 2+ /Cu + ions but K + ions only preferably replace the H + . We hypothesize that K + cannot enter into a small ring (6-membered ring) to replace a Cu 2+ /Cu + ion because of its large ion diameter. The displaced Cu 2+ /Cu + ions will transfer to adjacent unbonded Al site to form a CuAlO 2 species.