Effective Cu-Off Catalysts Synthesized Via Charge Density Mismatch for Low-Temperature Nh3-Scr Process

Abstract

The OFF zeolites were successfully synthesized for the first time using the charge density mismatch (CDM) strategy with 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 NOx using NH3 (NH3-SCR) reaction. Among Cux-OFF catalysts, Cu2.04-OFF exhibited the highest catalytic performance, achieving over 80% NOx conversion across a broad temperature range of 175-600 °C. Moreover, the catalytic performance of the Cu2.04-OFF catalyst decreased slightly at GHSVs reaching 200,000 and 400,000 h-1, and after hydrothermal aging of 750 and 850 °C. The physical properties, acidity and redox characteristics were thoroughly investigated using various characterization techniques. Notably, in situ DRIFTS analysis indicated that the Cu2.04-OFF catalyst predominantly operates through the Eley-Rideal (E-R) mechanism, utilizing NH3 as the absorbents in the NH3-SCR reaction (200 °C). The comprehensive results show that OFF zeolite synthesized by CDM method has outstanding practical application value in NH3-SCR reaction after copper exchange.

Keywords: selective catalytic reduction, Cu-OFF, ion exchanged method, NOx elimination, charge density mismatch