Kondratenko Evgenii V, Pérez-Ramírez Javier
Leibniz-Institut für Katalyse e. V. an der Universität Rostock, Aussenstelle Berlin, Richard-Willstätter-Strasse, 12 D-12489 Berlin, Germany.
J Phys Chem B. 2006 Nov 16;110(45):22586-95. doi: 10.1021/jp063492w.
The mechanism of direct N(2)O decomposition over Fe-ZSM-5 and Fe-silicate was studied in the temporal analysis of products (TAP) reactor in the temperature range of 773-848 K at a peak N(2)O pressure of ca. 10 Pa. Several kinetic models based on elementary reaction steps were evaluated to describe the transient responses of the reactant and products. Classical models considering oxygen formation via recombination of two adsorbed monoatomic oxygen species (*-O + -O --> O(2) + 2) or via reaction of N(2)O with adsorbed monoatomic oxygen species (N(2)O + -O --> O(2) + N(2) + ) failed to describe the experimental data. The best description was obtained considering the reaction scheme proposed by Heyden et al. (J. Phys. Chem. B 2005, 109, 1857) on the basis of DFT calculations. N(2)O decomposes over free iron sites () as well as over iron sites with adsorbed monoatomic oxygen species (-O). The latter reaction originates adsorbed biatomic oxygen species followed by its transformation to another biatomic oxygen species, which ultimately desorbs as gas-phase O(2). In line with previous works, our results confirm that the direct N(2)O decomposition is controlled by pathways leading to O(2). Our kinetic model excellently described transient data over Fe-silicalite and Fe-ZSM-5 zeolites possessing markedly different iron species. This finding strongly suggests that the reaction mechanism is not influenced by the iron constitution. The TAP-derived model was extrapolated to a wide range of N(2)O partial pressures (0.01-15 kPa) and temperatures (473-873 K) to evaluate its predictive potential of steady-state performance. Our model correctly predicts the relative activities of two Fe-FMI catalysts, but it overestimates the absolute catalytic activity for N(2)O decomposition.
在产物瞬态分析（TAP）反应器中，研究了773 - 848 K温度范围内、N₂O峰值压力约为10 Pa时，Fe-ZSM-5和铁硅酸盐上N₂O直接分解的机理。评估了基于基元反应步骤的几种动力学模型，以描述反应物和产物的瞬态响应。考虑通过两个吸附的单原子氧物种重组形成氧气（*-O + -O --> O₂ + 2）或通过N₂O与吸附的单原子氧物种反应形成氧气（N₂O + -O --> O₂ + N₂ + ）的经典模型无法描述实验数据。基于密度泛函理论（DFT）计算，采用Heyden等人（《物理化学杂志B》2005年，第109卷，1857页）提出的反应方案，得到了最佳描述。N₂O在自由铁位点（）以及带有吸附单原子氧物种（-O）的铁位点上分解。后一种反应产生吸附的双原子氧物种，随后转化为另一种双原子氧物种，最终以气相O₂形式解吸。与先前的研究一致，我们的结果证实N₂O的直接分解受生成O₂的途径控制。我们的动力学模型出色地描述了具有明显不同铁物种的铁硅酸盐和Fe-ZSM-5沸石上的瞬态数据。这一发现强烈表明反应机理不受铁组成的影响。将TAP衍生模型外推到广泛的N₂O分压（0.01 - 15 kPa）和温度（473 - 873 K）范围，以评估其对稳态性能的预测潜力。我们的模型正确预测了两种Fe-FMI催化剂的相对活性，但高估了N₂O分解的绝对催化活性。
