Decomposition and reduction of N2O over copper catalysts
Decomposition and reduction of N2O over copper catalysts
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DOI：
10.1016/s0926-3373(99)00049-1
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发表时间：
1999-09-20
影响因子：
22.1
通讯作者：
Vannice, MA
中科院分区：
文献类型：
--
作者：
Dandekar, A;Vannice, MA
研究了 Cu/碳、Cu/Al2O3、Cu/SiO2 和 Cu/ZSM-5 催化剂的 N2O 分解动力学，旨在监测实现 Cu 化学计量催化分解的要求并阐明载体在催化循环中的作用。与 Cu/ZSM-5 相比，碳非常有效的除氧能力导致 Cu/C 催化剂具有更高的初始活性和周转频率；然而，碳载体的快速气化限制了这些 Cu/C 催化剂的寿命。 Cu/Al2O3 和 Cu/SiO2 在低于 823 K 的温度下表现出非常低的分解活性；然而，向反应器进料流中添加 CO 或 H-2 显着降低了实现催化 N2O 还原所需的温度。对于所有催化剂，发现流出物流中的产物比率稳定在接近O-2/N-2（或CO2/N-2）= 1/2的化学计量比时的温度对应于O-2解吸或被碳去除的温度。这些催化剂在 173 K 下吸附的 CO 的 DRIFT 光谱表明，Cu+1 和 Cu+2 物质在活性相中共存，正如氧化还原机制所预期的那样，需要这两个位点之间的平衡。相比之下，失活催化剂的光谱表明，Cu 位点主要以 Cu+2 形式存在，只有非常小的 Cu+1 部分，因此表明在较低温度下在这些催化剂中观察到的失活主要是由于无法将 Cu+2 阳离子还原回 Cu+1 状态。从适用于每种催化剂的基本步骤序列导出的不同动力学速率表达式很好地拟合了 Cu/ZSM-5 和 Cu/Al2O3 上 N2O 分解以及碳和 CO 还原 N2O 的数据，并且它们产生了有意义的 N2O、O-2 和 CO 吸附焓和熵值。 (C) 1999 Elsevier Science B.V. 保留所有权利。
The kinetics of N2O decomposition were investigated over Cu/carbon, Cu/Al2O3, Cu/SiO2, and Cu/ZSM-5 catalysts with the intent of monitoring the requirements for achieving stoichiometric catalytic decomposition over Cu and elucidating the role of the support in the catalytic cycle. The very efficient oxygen scavenging capability of carbon led to higher initial activities and turnover frequencies on Cu/C catalysts compared to Cu/ZSM-5; however, rapid gasification of the carbon support limited the lifetime of these Cu/C catalysts. Very low decomposition activity was exhibited by Cu/Al2O3 and Cu/SiO2 at temperatures below 823 K; however, addition of CO or H-2 to the reactor feed stream significantly lowered the temperatures required to achieve catalytic N2O reduction. With all catalysts, the temperature at which the product ratio in the effluent stream stabilized near the stoichiometric ratio of O-2/N-2 (or CO2/N-2) = 1/2 was found to correspond to that at which O-2 either desorbs or is removed by carbon. DRIFT spectra of CO adsorbed at 173 K on these catalysts indicated that both Cu+1 and Cu+2 species coexist during the active phase, as expected for a redox mechanism requiring a balance between these two sites. In contrast, spectra of deactivated catalysts indicated that the Cu sites exist predominantly as Cu+2 species, with only a very small Cu+1 fraction, thus suggesting that the deactivation observed in these catalysts at lower temperatures is primarily due to the inability to reduce Cu+2 cations back to a Cu+1 state. Different kinetic rate expressions, derived from sequences of elementary steps appropriate for each catalyst, fit the data well for N2O decomposition on Cu/ZSM-5 and Cu/Al2O3 as well as N2O reduction by carbon and CO, and they yielded meaningful values for enthalpies and entropies of adsorption for N2O, O-2 and CO. (C) 1999 Elsevier Science B.V. All rights reserved.