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

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• 作者：M.N. Debbagh ; A. Bueno-Ló ; pez ; C. Salinas Mart&#xed ; nez de Lecea ; J. Pé ; rez-Ram&#xed ; rez
• 关键词：FeZSM-5 ; N₂O ; CO ; Reduction ; Direct decomposition ; Kinetics ; Rate law
• 刊名：Applied Catalysis A ; General
• 出版年：2007
• 期刊代码：4_0926860x
• 类别：ch
• 出版时间：31 July 2007
• 卷：327
• 期：1
• 页码：66-72
• 文件大小：624 K

摘要

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.