The reduction of NOx in the gas phase (in a NO-NO2-decane-water-O-2 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 NOx 300 ppm C10H22, 6.0% O-2, and O or 12.0% H2O at gas hourly space velocity values of 15 000-60 000 h(-1) and temperatures of 150-450 degrees C. Under the experimentally investigated reaction conditions, there was no N-2 formation in the bulk gas phase. Water vapor had little effect on the N-2 yield in decane-SCR of NOx. The kinetic description of the homogeneous system included reactions between NO2 and decane with the formation of NO, CO, and CO2 and a pseudocompound "C3H6O1.8" lumping all oxygenated, olefinic, 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 C3H6O1.8, yielding N-2, NO, CO, and CO2. 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 N-2 formation.