Influence of Ceria on the Dispersion and Reduction/Oxidation Behaviour of Alumina-Supported Copper Catalysts
Influence of Ceria on the Dispersion and Reduction/Oxidation Behaviour of Alumina-Supported Copper Catalysts
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DOI：
10.1006/jcat.1997.1842
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发表时间：
1997-11
影响因子：
7.3
通讯作者：
M. Fernández-García;E. Rebollo;A. G. Ruiz;J. Conesa;J. Soria
中科院分区：
文献类型：
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作者：
M. Fernández-García;E. Rebollo;A. G. Ruiz;J. Conesa;J. Soria
用透射电子显微镜结合电子衍射(ED)、红外光谱(IR)、电子自旋共振(ESR)、X射线光电子能谱(XPS)和质谱学-程序升温表面反应技术研究了NO在Cu/CeOx/Al_2O_3催化剂上的程序升温表面反应，以及在不含Ce或Cu的类似样品上的反应。透射电子显微镜显示，氧化的铜相优先在富CeO_3区域形核，导致含铜相的颗粒尺寸小于Al_2O_3负载体系中的颗粒尺寸，减少了CuAl_2O_4尖晶石的形成。在焙烧处理中形成的铜-Ce相互作用也对H_2还原过程中形成的金属铜相的烧结具有显著的稳定性。还原后，与Cu/Al_2O_3相比，含Ce样品表现出更高的抗NO将表面铜相二次氧化到Cu2+状态的能力。根据XPS-Ar+溅射数据，这可能与还原CeO2以类似于目前所接受的SMSi效应的方式对金属Cu的部分覆盖有关；含Ce的载体稳定Cu+态的能力也可能有助于这一行为。这种稳定的铜态出现在亚表面区域，并可能与一种新的相有关，该相被初步确定为(Ce，Cu)-Al钙钛矿。铜-铈的相互作用也影响了催化剂对NO的反应活性，增加了吸附物种的数量(部分通过解离机制)，从而导致低温NO和N_2/N_2O脱附，并改变了在吸附NO时形成的含有N-N键的表面物种(N_2/N_2O)的分解温度。提出CeO_2的加入有助于增强汽车尾气中铜对NO的还原消除作用。
A study using TEM combined with electron diffraction (ED), several spectroscopies (IR, ESR, XPS), and mass spectrometry-temperature programmed surface reaction of adsorbed NO is carried out on a Cu/CeOx/Al2O3catalyst and on similar specimens without Ce or Cu. TEM shows a preferential nucleation of the oxidized Cu phase on the ceria-rich regions, leading to a particle size in the Cu-containing phase smaller than that found in the Al2O3-supported system and decreasing the formation of the CuAl2O4spinel. The Cu–Ce interaction developed in the calcination treatment also gives significant stability against sintering of the metallic copper phase formed during H2reduction. After reduction, the Ce-containing sample shows higher resistance to reoxidation of the surface copper phase by NO to the Cu2+state (in comparison to Cu/Al2O3). On the basis of XPS-Ar+sputtering data, this may be related to partial coverage of the metallic Cu by reduced ceria in a way similar to that currently accepted for the SMSI effect; a capability of the Ce-containing support to stabilize the Cu+state may also contribute to this behaviour. This stable copper state appears in subsurface regions and is likely related to a new phase detected by TEM-ED and tentatively identified as a (Ce,Cu)–Al perovskite. The copper-cerium interaction affects also the reactivity of the catalyst towards NO, increasing (partly through a dissociative mechanism) the amount of adsorbed species which leads to low temperature NO and N2/N2O desorption, as well as shifting the decomposition temperatures of surface species containing N–N bonds (N2/N2O) formed upon NO adsorption. It is proposed that the addition of ceria may help to enhance the reductive elimination of NO by copper in automobile exhaust gases.