Effect of Water Vapor on Catalytic Decomposition of NO over Cu-ZSM-5: A Mechanism and Kinetic Study

Cu-ZSM-5 has great potential for the direct catalytic decomposition of NO in flue gas. However, NO conversion is significantly inhibited in the presence of water vapor, and the mechanism for this inhibition process has not been identified. In this study, a series of experiments are carried out to simulate the flue gas in coal-fired power plants. The reaction mechanism for NO decomposition and the corresponding kinetics are determined. The experimental results show that NO conversion clearly decreases as the water vapor content increases. A variety of characterization methods were applied to the samples treated with water vapor. Brunauer-Emmett-Teller shows the change from micro- to mesopores under the action of water vapor, while X-ray diffraction shows grain growth, fragmentation, and agglomeration under the action of water vapor. Scanning electron microscopy shows that the surface of the grains is corroded by water vapor, while ultraviolet-visible spectroscopy shows the presence of Al3+ in the condensate. Finally, Raman and Fourier transform infrared spectroscopy show that the skeleton structure of the catalyst is destroyed by water vapor. CuO is detected as a result of changes in the copper species, which is caused by the destruction of the skeleton structure. Furthermore, there is competition between NO and H2O in the adsorbing process. The steady-state kinetics of Cu-ZSM-5 show that the decomposition rate of NO increases with the increase in the NO concentration, [Cu-O-Cu](2+) dimer number, and chemical kinetic parameters. The reaction rate constant k(1) is positively correlated with the temperature. Additionally, there is a side reaction between the dimer and H2O, which can reduce the amount of dimer and the impact factor b. Finally, the reaction rate constant k1 and the impact factor b increase with an appropriately increasing temperature.