Cu-OFF/ERI zeolite: Intergrowth structure synergistically boosting NH3-SCR performance

Cu-SSZ-13 zeolite has been commercialized for selective catalytic reduction with ammonia (NH3-SCR) to remove NOx from diesel exhaust. As its synthesis usually requires toxic and costly organic templates, the discovery of alternative Cu-based zeolite catalysts with organotemplate-free synthesis and comparable or even superior NH3-SCR activity to Cu-SSZ-13 is of great academic and industrial significance. Herein, we, for the first time, demonstrated that the Cu-T catalyst with an intergrowth structure of offretite (OFF) and erionite (ERI) synthesized with organotemplate-free method showed better catalytic performance than Cu-ERI and Cu-OFF as well as Cu-SSZ-13. Structure characterizations and density functional theory (DFT) calculations indicated that the intergrowth structure promoted more isolated Cu2+ located at 6MR of intergrowth interface, resulting in a better hydrothermal stability of Cu-T than Cu-ERI and Cu-OFF. Strikingly, the low-temperature activity of Cu-T significantly increased after hydrothermal aging, while that of Cu-ERI and Cu-OFF substantially decreased. On the basis of in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) analysis and DFT calculations, the reason can be attributed to that the NH4NO3 formed on the CuxOy species within ERI polymorph of Cu-T underwent fast SCR reaction pathway with the assistance of Brønsted acid sites at the intergrowth interfaces under standard SCR reaction conditions. Significantly, Cu-T exhibited a wider temperature window at a catalytic activity over 90% than Cu-SSZ-13 (175 − 550 ℃ vs. 175 − 500 ℃ for fresh and 225 − 500 ℃ vs. 250 − 400 ℃ for hydrothermal treatment). This work provides a new direction for the design of high-performance NH3-SCR catalysts in terms of the interplay of intergrowth structure of zeolites.