Inhibiting the Formation of Toxic HCN Induced by C 3 H 6 Coexistence and Enhancing C 3 H 6 Resistance of Cu-Zeolite in the NH 3 -SCR Reaction.

The presence of light hydrocarbons (HCs) in diesel exhaust, specifically C 3 H 6 , significantly affects the performance of the state-of-the-art Cu-SSZ-13 zeolite NH 3 -SCR catalysts. It also leads to the formation of highly toxic HCN, posing risks to the environment and human health. In this work, the highly toxic HCN formation is inhibited, and the C 3 H 6 resistance of Cu-SSZ-13 is improved by secondary metal modification via doping with rare earth/transition metal elements. Upon introduction of C 3 H 6 , the activity of Cu-SSZ-13 significantly decreases at medium-high temperatures. This is primarily due to the competitive reaction between C 3 H 6 and NH 3 , which compete for the NH 3 reductant required in the NH 3 -SCR reaction, resulting in the production of HCN. The unfavorable effect is alleviated on the modified catalysts due to their enhanced oxidation capabilities toward C 3 H 6 and the HCHO intermediate, facilitating the complete oxidation of C 3 H 6 to CO x . This inhibits the undesirable partial oxidation reaction between C 3 H 6 and NH 3 , thereby improving the activity of Cu-SSZ-13 at medium to high temperatures and significantly reducing the formation of highly toxic HCN.