Design, Synthesis, and Insights into the Redox Mechanism of Highly Efficient One-Pot Cu-ZSM-5 Catalysts for the Reduction of NO_<i>x</i> by NH₃-SCR at Low Temperatures

Abstract

Cu-ZSM-5 zeolites exhibit promising NH 3 -SCR activity in a wide temperature window. The current challenges in preparing Cu-ZSM-5 are reducing the cost and simplifying the preparation process. The one-pot method using the Cu-amine complex as the template is an excellent strategy for solving the above problems. However, the above method is still lacking in preparing Cu-ZSM-5. In this work, a one-pot method using the Cu-(EDA) 2 complex as the template is developed to prepare the Cu-ZSM-5-O catalyst. According to the fundamental measurements, the high dispersion of copper(II) species, appropriate acidity, and Cu + species are in favor of the NH 3 -SCR reaction. Among one-pot catalysts, Cu 1.8 -ZSM-5-O shows excellent NH 3 -SCR performance at low temperatures (NO conversion of about 87.5% at 150 °C and N 2 selectivity above 95% over the entire temperature window). The boosting activity at low temperatures of one-pot catalysts is probably assigned to abundant [Cu(OH)] + species and appropriate amounts of Cu + species in Cu-ZSM-5-O. Moreover, the variable-temperature EPR and subsequent computer simulation are used first to quantify the content of [Cu(OH)] + species in Cu-ZSM-5-O. The NH 3 -SCR mechanism at low temperatures (150 °C) on [Cu(OH)] + species is also investigated by in situ DRIFT spectra and DFT calculations, which mainly follow the Eley–Rideal route. A complete catalytic cycle of the SCR reaction was proposed based on the [Cu(OH)] + species by DFT calculations. Our results suggest that [Cu(OH)] + species contribute to the adsorption and activation of NH 3, thus boosting the catalytic performance.