Structure sensitivity of the low-temperature water-gas shift reaction on Cu-CeO2 catalysts
Structure sensitivity of the low-temperature water-gas shift reaction on Cu-CeO2 catalysts
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DOI：
10.1016/j.cattod.2011.09.008
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发表时间：
2012-01-17
期刊：
影响因子：
5.3
通讯作者：
Flytzani-Stephanopoulos, Maria
中科院分区：
文献类型：
--
作者：
Si, Rui;Raitano, Joan;Flytzani-Stephanopoulos, Maria
研究了不同制备方法制备的纳米Cu-CeO 2催化剂对水煤气变换反应的结构敏感性。在氧化铈的表面上，存在不同的CuOx结构。我们在这里表明，只有强烈结合的Cu-[O-x]-Ce物种，可能与氧化铈的表面氧空位，是积极的催化低温WGS反应。弱结合的CuOx团簇和CuO纳米颗粒是反应中的旁观物种。掺杂二氧化铈表面的孤立的Cu 2+离子本身不具有活性，但它们是重要的，因为它们产生氧空位，并且可以用作铜的储存器以补充通过浸出或烧结去除的表面Cu。因此，允许Cu在二氧化铈中广泛溶解的合成技术如共沉淀应优于浸渍、沉积-沉淀、离子交换或另一种两步法，由此将铜前体添加到已经制备的二氧化铈纳米晶体中。对于不同结构的合成，我们使用了两种方法：均相共沉淀（CP），涉及六亚甲基四胺作为沉淀剂和pH缓冲液;和沉积沉淀（DP）技术。在后一种情况下，首先在纳米级合成具有不同形状（棒、立方体）的二氧化铈载体，以研究对反应的任何潜在形状效应。Cu-CeO 2催化剂具有不同的铜含量高达约。20原子%制备了CeO 2的间接形状效应，表现为形成氧空位的倾向，并强烈地结合在活性形式的铜，被建立; i。e.水煤气变换反应对结构不敏感。在无产物（2%CO-10%H2O）气体混合物中，所有样品上的反应的表观活化能相似，为50 +/-10kJ/mol。(C)2011 Elsevier B. V.保留所有权利。
We have investigated the structure sensitivity of the water-gas shift (WGS) reaction on Cu-CeO2 catalysts prepared at the nanoscale by different techniques. On the surface of ceria, different CuOx structures exist. We show here that only the strongly bound Cu-[O-x]-Ce species, probably associated with the surface oxygen vacancies of ceria, are active for catalyzing the low-temperature WGS reaction. Weakly bound CuOx clusters and CuO nanoparticles are spectator species in the reaction. Isolated Cu2+ ions doping the ceria surface are not active themselves, but they are important in that they create oxygen vacancies and can be used as a reservoir of copper to replenish surface Cu removed by leaching or sintering. Accordingly, synthesis techniques such as coprecipitation that allow for extensive solubility of Cu in ceria should be preferred over impregnation, deposition-precipitation, ion exchange or another two-step method whereby the copper precursor is added to already made ceria nanocrystals. For the synthesis of different structures, we have used two methods: a homogeneous coprecipitation (CP), involving hexamethylenetetramine as the precipitating agent and the pH buffer; and a deposition-precipitation (DP) technique. In the latter case, the ceria supports were first synthesized at the nanoscale with different shapes (rods, cubes) to investigate any potential shape effect on the reaction. Cu-CeO2 catalysts with different copper contents up to ca. 20 at.% were prepared. An indirect shape effect of CeO2, manifested by the propensity to form oxygen vacancies and strongly bind copper in the active form, was established; i. e. the water-gas shift reaction is not structure-sensitive. The apparent activation energy of the reaction on all samples was similar, 50 +/- 10 kJ/mol, in a product-free (2% CO-10% H2O) gas mixture. (C) 2011 Elsevier B.V. All rights reserved.