The First Study of SCR of NO _x by Acetylene in Excess Oxygen

Acetylene as a reducing agent for the selective catalytic reduction (C₂H₂-SCR) of NO in the presence of excess oxygen on various Ce-exchanged zeolites was investigated for the first time. Under the conditions of 1600 ppm NO, 800 ppm C₂H₂, and 9.95 % O₂ in He, the Ce-H-ZSM-5 (Si/Al=25) catalyst shows about 83% NO conversion to N₂ at the temperatures ranged from 300 to 350 °C. It is followed by the other zeolites in the activity order of Ce-H-Y (Si/Al=2.5), Ce-H-_ (Si/A1=20∼30), and Ce-H-SAPO (Si/Al=34), Ce-H-5A (Si/Al=12). Almost no NO conversion was obtained over Ce-Na-ZSM-5 (Si/Al=25) and Na-ZSM-5 (Si/Al=25) catalyst samples. The Conversion of NO to N₂ increased with O₂ concentration in the range of 0.1 ∼ 9.95% over the CeH-ZSM-5 (Si/Al=25) catalyst. It is suggested that O₂ plays an important role in the C₂H₂-SCR of NO reaction, by oxidizing NO to NO₂ on acid sites in assistant with cerium species of the catalyst. A large amount of CO, which seems to be in proportion with the NO conversion to N₂, was produced. Long-term experiments up to 56 h combined with a excursion of the reaction temperature up to 650 °C over the Ce-H-ZSM-5 (Si/A1=25) confirmed the catalyst’s durable performance under the reaction conditions. It is found that the de-NO _x activity of Ce-H-ZSM-5 catalyst can be enhanced by the presence of 50 ppm of sulfur dioxide in the dry-feed reaction conditions.