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

The mechanism of the selective catalytic reduction of NO by NH 3 (NH 3 –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 NH 3 . DFT calculations suggest that the reduction half-cycle of NH 3 –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 Cu II sites are responsible for the activation of NO into NO + /HONO intermediates, which then react with NH 3 to afford N 2 and H 2 O over BASs.