NO Decomposition and Selective Catalytic Reduction of NO over Cu-ZSM-5 Zeolite

More attention to Cu-ZSM-5 zeolite has been paid due to its excellent catalytic activities in removal of NO, and the process it concerned is non-polluting. In this review, the reaction mechanism and catalyst improvement of NO decomposition, selective catalytic reduction of NO with ammonia (NH3-SCR-NO) and with hydrocarbons (CH-SCR-NO) over Cu-ZSM-5 zeolite are summarized. The possible developing orientations in the field of removal of NO over Cu-ZSM-5 zeolite are also prospected. Direct catalytic decomposition of NO to N-2 and O-2 has been recognized as the most attractive method for removal of NO, which involves redox process of Cu+ and formation of N2O. NH3-SCR-NO reaction is one of the most efficient and widely-used techniques. Firstly, NO is oxidized to NO2, and then NH4NO3 is formed from the reaction of NO2 and NH3. Finally, NH4NO3 reacts with NO generating N-2. CH-SCR-NO reaction over Cu-ZSM-5 zeolite is an efficient way for the treatment of automobile-exhaust pollution. The formation of key intermediates such as isocyanate and cyanide species is a necessary process during CH-SCR-NO reaction. However, Cu-ZSM-5 zeolite suffers from poor hydrothermal stability and high sulfur dioxide (SO2) poisoning property which have suppressed its industrial applications. Introduction of a second metal and fabrication of monolithic catalyst can significantly improve the catalytic performance of Cu-ZSM-5 zeolite. The systematic understanding of reaction mechanism is beneficial to the improvement of Cu-ZSM-5 zeolite and also important for the design of novel, efficient, environmentally-friendly catalysts.