Synthesis of zeolite UZM-35 and catalytic properties of copper-exchanged UZM-35 for ammonia selective catalytic reduction

Abstract

The synthesis of zeolite UZM-35 with the MSE topology and the catalytic properties of copper-exchanged UZM-35 (Cu-UZM-35) for the selective catalytic reduction of NOx with NH3 (NH3-SCR) are presented. When the simple dimethyldipropylammonium cation is used as an organic structure-directing agent together with Na+ and K+, crystallization of pure UZM-35 is very sensitive not only to the types of Al and Si sources employed, but also to the SiO2/Al2O3 and K2O/(Na2O+K2O) ratios in the synthesis mixture. In the temperature range studied, fresh Cu-UZM-35 shows comparable deNOx performance to fresh Cu-SSZ-13, the best NH3-SCR catalyst known to date. When hydrothermally aged at 750°C, although the latter catalyst outperforms the former one, the operating temperature window of Cu-UZM-35 is considerably wider than that of Cu-SSZ-13. Like Cu-beta, Cu-UZM-35 also produces a higher amount of N2O during SCR than Cu-SSZ-13 and Cu-ZSM-5. However, it shows a significantly lower NH3 oxidation activity than Cu-SSZ-13 and Cu-ZSM-5. The overall characterization results of this study demonstrate the highly stable nature of framework Al atoms in the large-pore zeolite UZM-35 and their strong interactions with Cu2+ ions. This may lead to a moderate alteration of exchanged Cu2+ ions to CuOx and CuAl2O4 phases at high temperatures, thus rendering Cu-UZM-35 hydrothermally stable during NH3-SCR.