Kinetics of the N2O + CO reaction over steam-activated FeZSM-5 Original Research Article

The kinetics of the N2O reduction by CO as well as the direct N2O decomposition have been investigated over steam-activated FeZSM-5. To this end, steady-state experiments at different temperatures, partial reactant pressures, molar feed N2O/CO ratios, and space times were carried out in an integral fixed-bed micro-reactor. Different empirical and microkinetic models were evaluated in order to describe the experimental data and derive quantitative kinetic information. Depending on the molar feed CO/N2O ratio and temperature, the reduction occurs alone in the catalyst bed or simultaneously with direct N2O decomposition. The orders for N2O and CO in the N2O + CO reaction are 0.51 and 0.72, respectively, in contrast with the characteristic first-order behaviour of the direct N2O decomposition. The latter can be properly described by a two-step oxygen transfer mechanism. The scavenging mechanism (Eley-Rideal type), where gas-phase CO effectively eliminates adsorbed atomic oxygen properly describes the N2O + CO reaction. The removal of O* by CO is two orders of magnitude faster than by N2O, but the elimination of O* remains as the rate-determining step. The N2O activation generating adsorbed oxygen is 2–8 times faster than the O* elimination by CO. Elimination of O* by CO is more sensitive to temperature than N2O activation. The elementary step mechanism has been used to predict the fraction of free/oxidised sites. The inlet concentration of CO and temperature determines the degree of reduction of the catalyst surface. The obtained activation energies in direct N2O decomposition (141 kJ mol−1) and N2O reduction by CO (62 kJ mol−1) were in excellent agreement with values reported in the literature.