Mechanism of Standard NH3–SCR over Cu-CHA via NO+ and HONO Intermediates

The mechanism of the selective catalytic reduction of NO by NH3 (NH3–SCR) over Cu-CHA zeolite was investigated by in situ/operando IR experiments collaborated with density functional theory (DFT) calculations. Operando IR experiments under transient conditions show the formation of NO+ intermediate and its reaction with NH3. DFT calculations suggest that the reduction half-cycle of NH3–SCR occurs via NO+/HONO intermediates with Cu sites and Brønsted acid sites (BASs) both playing important roles. In the proposed reduction half-cycle, the CuII sites are responsible for the activation of NO into NO+/HONO intermediates, which then react with NH3 to afford N2 and H2O over BASs.