Controlling Selectivity in Unsaturated Aldehyde Hydrogenation Using Single-Site Alloy Catalysts
Controlling Selectivity in Unsaturated Aldehyde Hydrogenation Using Single-Site Alloy Catalysts
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DOI：
10.1021/acscatal.9b02547
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发表时间：
2019-10-01
期刊：
影响因子：
12.9
通讯作者：
Zaera, Francisco
中科院分区：
文献类型：
--
作者：
Cao, Yueqiang;Chen, Bo;Zaera, Francisco
催化的选择性是许多工业过程的关键，但往往难以控制。一种很有前景的方法是使用所谓的单原子催化剂，即在第二相中分离出一种催化成分，以增加一个键，否则无法获得功能。在这里，我们报道了使用由铜纳米粒子内稀释的Pt单原子组成的金属合金来选择性地促进不饱和醛中C=O键的氢化，这是精细化学制造中感兴趣的反应。我们的理论基础是，Cu表面可能更倾向于C=O而不是C=C与氢原子的加氢步骤，但可能需要Pt位点来促进分子氢的初始活化，这一理论得到了动力学催化实验的证实。然而，基础表面科学研究和量子力学计算表明，对观察到的催化性能的解释更为微妙。首先，使用一氧化碳的滴定实验未能识别催化剂表面可接近的Pt原子，这表明它们的催化作用可能涉及邻近Cu原子的间接电子变化。此外，红外吸收和x射线光电子能谱结果表明，金属纳米颗粒表面存在一层薄薄的氧化铜层。最后，确定了cu基催化剂的加氢选择性可能部分解释为它们倾向于通过末端氧原子键合不饱和醛，但也受到反应物和产物之间竞争吸附的影响。单原子合金催化剂似乎确实有助于加氢催化的选择性，但需要更多的原位（或operando）表征实验来更好地了解它们是如何运作的。
Selectivity in catalysis is key to many industrial processes, yet it is often difficult to control. One promising approach is to use so-called single-atom catalysts, whereby one catalytic component is isolated within a second phase to add a key but otherwise unavailable functionality. Here, we report the use of metal alloys consisting of Pt single atoms diluted within Cu nanoparticles to selectively promote the hydrogenation of C=O bonds in unsaturated aldehydes, a reaction of interest in fine chemical manufacturing. Our rationale, that Cu surfaces may favor C=O over C=C hydrogenation steps with atomic hydrogen but may require Pt sites to promote the initial activation of molecular hydrogen, was corroborated by kinetic catalytic experiments. However, fundamental surface science studies and quantum mechanics calculations showed that the explanation for the observed catalytic performance is more nuanced. For one, titration experiments using carbon monoxide failed to identify Pt atoms accessible on the surface of the catalysts, suggesting that their catalytic contribution may involve indirect electronic changes on neighboring Cu atoms. In addition, infrared absorption and X-ray photoelectron spectroscopy results identified the existence of a thin Cu oxide layer covering the metallic nanoparticles. Finally, it was determined that hydrogenation selectivity with Cu-based catalysts may be explained in part by their preference for bonding unsaturated aldehydes via the terminal oxygen atom but is also affected by competitive adsorption among the reactants and products. Single-atom alloy catalysts appear to indeed help with selectivity in hydrogenation catalysis, but more in situ (or operando) characterization experiments are needed to better understand how they operate.