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 Bronsted 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 N-2 and H2O over BASs.

Automated summary

The mechanism of the selective catalytic reduction of NO by NH3 over Cu-CHA zeolite was investigated using in situ/operando IR experiments and density functional theory (DFT) calculations. Experimental results showed the formation of NO+ intermediates, while DFT calculations indicated that Cu sites and Brønsted acid sites played important roles in the reduction half-cycle of NH3-SCR. In this proposed half-cycle, CuII sites activated NO into NO+/HONO intermediates, which then reacted with NH3 over Brønsted acid sites to produce N-2 and H2O.