A study of Cu-SAPO-34 catalysts for SCR of NOx by ammonia

H-SAPO-34 and Cu-SAPO-34 catalysts have been synthesized by a hydrothermal method using ultrasound and diethylamine (DEA) as structural directing agent. Copper has been incorporated in a one-pot process (2 and 4% w/w) as a complex with tetraethylenepentamine (TEPA) in the initial synthesis gel. The catalysts have been characterized by XRD, SEM, skeletal transmission IR, DR UV–Vis spectroscopy, IR studies of the surface OH groups and of adsorbed probe molecules. In the case of our Cu-SAPO-34 catalysts, which are active in the SCR of NOx by ammonia, Cu2+ ions are present, mainly located in the interior of the cavities and easily reducible to Cu+ by simple outgassing at 500 °C. Together with these sites, protonic sites are also still present in the cavities, in part as free OH groups (split band at 3625 and 3600 cm−1) and in part as H-bonded species (broad absorption in the 3800-2000 cm−1 region). Thus, the active catalyst presents a close position of Brønsted sites and Cu+/Cu2+ redox sites.