Kinetic experiments and modeling of a complex DeNO system: Decane selective catalytic reduction of NO_x in the gas phase and over an Fe-MFI type zeolite catalyst

The reduction of NO_x in the gas phase (in a NO-NO ₂-decane-water-O₂ mixture) and over a Fe-MFI type zeolite catalyst was extensively studied under a wide range of temperatures, gas hourly space velocities, and concentrations. The Fe-MFI zeolite (Si/Al 12.5 and Fe/Al 0.31) was prepared by solid-state ion exchange. The decane selective catalytic reductions (decane-SCRs) of NO and NO₂ were carried out with a reaction mixture consisting of 1000 ppm NO_x, 300 ppm C ₁₀H₂₂, 6.0% O₂, and 0 or 12.0% H₂O at gas hourly space velocity values of 15 000-60 000 h^-1 and temperatures of 150-450 °C. Under the experimentally investigated reaction conditions, there was no N₂ formation in the bulk gas phase. Water vapor had little effect on the N₂ yield in decane-SCR of NO _x. The kinetic description of the homogeneous system included reactions between NO₂ and decane with the formation of NO, CO, and CO₂ and a pseudocompound "C₃H₆O _1.8" lumping all oxygenated, olefmic, and paraffinic hydrocarbon products. The heterogeneous system accounts for two distinct functions of the Fe-loaded zeolite catalyst: NO oxidation and SCR of NO₂ with decane and C₃HeO_1.8, yielding N₂, NO, CO, and CO ₂. This kinetic description yielded a good fit of experimental data. The rates of heterogeneous reactions were higher than the rates of homogeneous reactions by 1-3 orders of magnitude. Among catalytic reactions, the NO formation out of NO₂ was the fastest reaction, which is the main reason for the relatively low nitrogen yield (<40%). The NO oxidation function of the Fe-MFI catalyst is insufficient, while a high oxidation rate is critical for improved N₂ formation.