Effective Cu-OFF catalysts synthesized via charge density mismatch for low-temperature NH3-SCR process

The Offretite (OFF) zeolites were successfully synthesized for the first time using the Charge Density Mismatch (CDM) strategy, employing three different organic structure directing agents (OSADs) and three inorganic structure directing agents (ISDAs). Subsequently, OFF zeolites were ion-exchanged with varying amounts of Cu species and evaluated for their performance in the selective catalytic reduction of NO_x using NH₃ (NH₃-SCR). Among the Cu_x-OFF catalysts, Cu_2.04-OFF exhibited the highest catalytic performance, achieving over 80% NO_x conversion across a broad temperature range of 175–600 °C. Moreover, the catalytic performance of the Cu_2.04-OFF catalyst decreased slightly at GHSVs reaching 200,000 and 400,000 h⁻¹, and after hydrothermal aging of 750. The physical properties, acidity and redox characteristics of the catalysts were comprehensively analyzed using various characterization techniques. Notably, in situ DRIFTS analysis indicated that the Cu_2.04-OFF catalyst predominantly operates through the Eley-Rideal (E-R) mechanism, utilizing NH₃ as the absorbents in the NH₃-SCR reaction (200 °C). The detailed results demonstrate that OFF zeolite synthesized using the CDM method exhibits exceptional practical potential in NH₃-SCR reactions after copper exchange.