Inhibiting the Formation\nof Toxic HCN Induced by C<sub>3</sub>H<sub>6</sub> Coexistence and\nEnhancing C<sub>3</sub>H<sub>6</sub> Resistance of Cu-Zeolite in the\nNH<sub>3</sub>–SCR\nReacti

The presence of light hydrocarbons (HCs) in diesel exhaust,\nspecifically\nC<sub>3</sub>H<sub>6</sub>, significantly affects the performance\nof the state-of-the-art Cu-SSZ-13 zeolite NH<sub>3</sub>–SCR\ncatalysts. It also leads to the formation of highly toxic HCN, posing\nrisks to the environment and human health. In this work, the highly\ntoxic HCN formation is inhibited, and the C<sub>3</sub>H<sub>6</sub> resistance of Cu-SSZ-13 is improved by secondary metal modification <i>via</i> doping with rare earth/transition metal elements. Upon\nintroduction of C<sub>3</sub>H<sub>6</sub>, the activity of Cu-SSZ-13\nsignificantly decreases at medium-high temperatures. This is primarily\ndue to the competitive reaction between C<sub>3</sub>H<sub>6</sub> and NH<sub>3</sub>, which compete for the NH<sub>3</sub> reductant\nrequired in the NH<sub>3</sub>–SCR reaction, resulting in the\nproduction of HCN. The unfavorable effect is alleviated on the modified\ncatalysts due to their enhanced oxidation capabilities toward C<sub>3</sub>H<sub>6</sub> and the HCHO intermediate, facilitating the\ncomplete oxidation of C<sub>3</sub>H<sub>6</sub> to CO<i><sub>x</sub></i>. This inhibits the undesirable partial oxidation\nreaction between C<sub>3</sub>H<sub>6</sub> and NH<sub>3</sub>, thereby\nimproving the activity of Cu-SSZ-13 at medium to high temperatures\nand significantly reducing the formation of highly toxic HCN.