MECHANISM OF THE LEAN NOX REACTION OVER CU/ZSM-5
MECHANISM OF THE LEAN NOX REACTION OVER CU/ZSM-5
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DOI：
10.1016/0926-3373(93)80028-c
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发表时间：
1993-03-15
影响因子：
22.1
通讯作者：
WALKER, AP
中科院分区：
文献类型：
--
作者：
ANSELL, GP;DIWELL, AF;WALKER, AP
瞬态技术（包括TAP、产物的时间分析）已用于探索Cu/ZSM-5上贫NO（x）反应的机理。在存在和不存在氧的情况下，通过Cu/ZSM-5对丙烯和一氧化氮的活化已经由TAP研究以阐明参与氮的形成的还原物种的性质。无论氧存在与否，丙烯在沸石上转化为长寿命（富碳）物质，并且正是这些沉积的焦炭物质在该催化剂体系中充当还原剂。焦炭还原一氧化氮的能力因氧的存在而显著增强。氧的关键作用似乎是诱导产生的吸附态的NO（x）的交换铜网站，这些NO2型物种存在于高贫NO（x）活性的温度特征。在贫燃料（氧化性）废气下的程序升温反应期间，一氧化氮和丙烯都保留在较低温度下;随着温度升高，丙烯保留（作为焦炭）和总氧化开始竞争。然而，在表面上仍然存在足够的还原物质以允许-NO2物质的大量还原，因为后者接近其热稳定性的极限。
Transient techniques (including TAP, temporal analysis of Products) have been used to probe the mechanism of the lean NO(x) reaction over Cu/ZSM-5. The activation of propene and nitric oxide by Cu/ZSM-5, in the presence and absence of oxygen, have been investigated by TAP to elucidate the nature of the reducing species involved in the formation of nitrogen. Propene is converted to long-lived (carbon-rich) species on the zeolite whether oxygen is present or not, and it is these deposited coke species which act as the reductant in this catalyst system. The ability of the coke to reduce nitric oxide is significantly enhanced by the presence of oxygen. The crucial role of the oxygen appears to be to induce the generation of an adsorbed state of NO(x) on the exchanged-Cu sites; these NO2-type species exist at temperatures characteristic of high lean NO(x) activity. During temperature-programmed reaction under a fuel-lean (oxidising) exhaust-gas, both nitric oxide and propene are retained at lower temperatures; as the temperature rises, so propene retention (as coke) and total oxidation begin to compete. However, there are sufficient reducing species still present on the surface to allow substantial reduction of the -NO2 species, as the latter approach their limit of thermal stability.