Selective Catalytic Reduction Of NO With Hydrocarbons Over H-ZSM-5 Catalysts

Presently, the most significant problem is the removal of nitrogen O_xides. In order to protect the earth and human from the pollution of NO_x (the concentrate of NO is 95%), a variety of approaches have been explored in the past few years and recently selective catalytic reduction of NO_x by hydrocarbons (HC-SCR of NO_x) have received a great deal of attention.Using acetylene as a reductant and modified zeolites as catalysts in SCR of NO_x with the presence of excess O_xygen under 75, OOOh^-1 was investigated. The main experimental results and conclusions are summarized as follows:By comparision of various reductants, such as CH₄, C₂H₄ and C₂H₂, it has been found that C₂H₂ is more easily activated than CH₄ and C₂H₄, so the study of acetylene as a reductant for NO-SCR has both practical and academic importance.By comparision of the activities of H-ZSM-5 , H-X, H-Y and H- β zeolites in C₂H₂-SCR of NO, it has been found that the H-ZSM-5 zeolite has the higher activities and selectivities than other zeolites. Metal ion exchanged H-ZSM-5 zeolites haven't improved the activities of pure H-ZSM-5 catalyst.H-ZSM-5 loaded with SO₄^2-/ZrO₂ catalysts exhibite high activities and selectivities in the SCR of NO with acetylene at a high space velocity of 75 000 h^-1. Loading SO₄^2-/ZrO₂ on H-ZSM-5 improves the long-time durability and water tolerance.The crystalline structure and surface acidity of SO₄^2-/ZrO₂/H-ZSM-5 catalysts have beenexamined. The results show that solid superacid didn't change the zeolite structure, while increase the number of Lewis acid site, which can facilitate the SCR of NO with acetylene.The surface intermediate species on Co-H-ZSM-5 from TPD and TPR have been invesgated. The result shows that the decomposion of surface intermediate species or the reaction beteen it and NO/O2 on Co-H-ZSM-5 catalyst may be the main approach for C2H2-SCR of NO.