Insights on Copper, Manganese, and Nickel/ZSM-5 catalytic mechanisms for nitric oxides selective reduction with ammonia

The elucidation of the selective catalytic reduction mechanisms over state-of-the-art metal-promoted zeolites is essential for nitric oxides removal in automobile and stationary source applications. In this work, H/ZSM-5 catalysts modified with transition metals, including copper, manganese, nickel, were prepared by using an incipient wetness impregnation method evaluated ammonia. Results indicate that copper/ZSM-5 exhibits highest activity, > 90% oxide conversion at a broad operation temperature window (221–445 °C). profiles nickel/ZSM-5 shows two peaks correspond to weak activity among catalysts; low-temperature peak (290 °C) was induced nickel clusters dispersed on ZSM-5 surface, while high-temperature (460 assigned bulk oxides. size granular monoxide crystallites exposed (2 0 2) plane 2–30 nm, as confirmed Scanning electron microscopy, X-ray diffraction, Transmission microscope measurements. Temperature-programmed reductions hydrogen results testified copper cations, main species contributing reduction, reduced via Cu2+/Cu+→Cu0 Ni2+→Ni0 nickel/ZSM-5, respectively, manganese/ZSM-5, Mn3+ manganese Mn2+ hydrogen. Particularly, temperature-programmed desorption coupled mass spectrometer (TPD-MS) situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) comprehensively used reveal relationship between zeolite structure catalysts’ properties improving reduction. These confirm ammonia adsorbed activated both Brønsted Lewis acid sites. nitrous desorbs stages during oxide-TPD-MS measurements, corresponding bounded amorphous strongly metal oxides, respectively. process follows L-H mechanism low temperatures, which molecules catalyst surface. rates reached maximum value 1.8 × 108 (218 °C), 6.4 107 (227 3.9 s−1 (235 /ZSM-5,