Effects of copper content in Cu-SAPO-34 on its catalytic performance in NH₃-SCR of NO_x

A series of Cu-SAPO-34 catalysts with various Cu contents were prepared by using different kinds of ammonium salts and adjusting Cu²⁺ ion exchange time; their catalytic performance and hydrothermal stability in selectively catalytic reduction of NO_x with NH₃ (NH₃-SCR) were investigated. The results showed that Cu²⁺ ions are the predominant active sites in Cu-SAPO-34 for the NH₃-SCR of NO_x. With the increase of Cu content, the activity of Cu-SAPO-34 at low temperature is increased at first and then decreased. With a Cu content of 2.37%, the Cu-SAPO-34 catalyst exhibits the best low temperature activity; over it, the conversion of NO_x is higher than 80.0% at 185 ℃ and may even reach 98.7%. ICP, H₂-TPR, FT-IR and NH₃-TPD results illustrated that the introduction of Cu into SAPO-34 leads to an addition of new adsorption sites for ammonia, an increase of Lewis acid sites and a decrease of the adsorption strength of NH₃ on SAPO-34. However, a further increase of Cu loading (e.g. 2.90%) results in a decrease of Cu-SAPO-34 activity in SCR, which may be ascribed to the replacement of H in Si-OH-Al by Cu²⁺ that hinders the adsorption, storage and migration of NH₃ in NH₃-SCR. In addition, excessive loading of Cu is probably detrimental to the hydrothermal stability of the Cu-SAPO-34 catalyst.