Enhanced Hydrothermal Stability of Cu/SSZ-39 with Increasing Cu Contents, and the Mechanism of Selective Catalytic Reduction of NO

Cu/SSZ-39 is an alternative highly effective catalyst for selective catalytic reduction of NOx compounds in Diesel exhaust besides Cu/SSZ-13. The hydrothermal stability of Cu/SSZ-39 exhibits an obvious dependency on Cu contents. Further experiment evidence reveals a mutual protective effect between Cu2+ ion species and framework tetrahedral Al atoms upon hydrothermal treatments. Rietveld refinement has revealed that ionic Cu species mainly locate on the face of double 6 ring (d6r) units of AEI framework. With increasing Cu contents, the amount of highly stable isolated Cu2+ ions increases. In consequence, the stability of framework Al atoms under hightemperature hydrothermal conditions is enhanced. Furthermore, in situ DRIFTS suggests a mixed Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanism for SCR reactions over this catalyst at low temperatures, where NH4NOx (x = 2 or 3) molecules are identified as key intermediates.