Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 55, 20125, Milano, Italy.
Chem Soc Rev. 2018 Nov 12;47(22):8474-8502. doi: 10.1039/c8cs00152a.
Model systems are very important to identify the working principles of real catalysts, and to develop concepts that can be used in the design of new catalytic materials. In this review we report examples of the use of model systems to better understand and control the occurrence of charge transfer at the interface between supported metal nanoparticles and oxide surfaces. In the first part of this article we concentrate on the nature of the support, and on the basic difference in metal/oxide bonding going from a wide-gap non-reducible oxide material to reducible oxide semiconductors. The roles of oxide nanostructuring, bulk and surface defectiveness, and doping with hetero-atoms are also addressed, as they are all aspects that severely affect the metal/oxide interaction. Particular attention is given to the experimental measures of the occurrence of charge transfer at the metal/oxide interface. In this respect, systems based on oxide ultrathin films are particularly important as they allow the use of scanning probe spectroscopies which, often in combination with other measurements and with first principles theoretical simulations, allow full characterization of small supported nanoparticles and their charge state. In a few selected cases, a precise count of the electrons transferred between the oxide and the supported nanoparticle has been possible. Charge transfer can occur through thin, two-dimensional oxide layers also thanks to their structural flexibility. The flow of charge through the oxide film and the formation of charged adsorbates are accompanied in fact by a substantial polaronic relaxation of the film surface which can be rationalized based on electrostatic arguments. In the final part of this review the relationships between model systems and real catalysts are addressed by discussing some examples of how lessons learned from model systems have helped in rationalizing the behavior of real catalysts under working conditions.
模型系统对于识别实际催化剂的工作原理以及开发可用于设计新型催化材料的概念非常重要。在这篇综述中，我们报告了使用模型系统来更好地理解和控制负载金属纳米颗粒与氧化物表面之间电荷转移发生的实例。本文的第一部分集中讨论了载体的性质，以及从宽带隙不可还原氧化物材料到可还原氧化物半导体的金属/氧化物键合的基本差异。氧化物纳米结构、体相和表面缺陷以及杂原子掺杂的作用也得到了探讨，因为它们都是严重影响金属/氧化物相互作用的因素。特别关注了在金属/氧化物界面处电荷转移发生的实验测量。在这方面，基于氧化物超薄膜的系统尤为重要，因为它们允许使用扫描探针光谱学，通常与其他测量和第一性原理理论模拟相结合，可以对负载的小纳米颗粒及其电荷状态进行全面表征。在少数几个选定的情况下，已经有可能精确地计算出氧化物和负载纳米颗粒之间转移的电子数。电荷转移也可以通过二维氧化物薄层发生，这要归功于它们的结构灵活性。电荷通过氧化物薄膜的流动和带电荷的吸附物的形成伴随着薄膜表面的大量极化子弛豫，这可以基于静电论证来合理化。在这篇综述的最后一部分，通过讨论从模型系统中获得的经验教训如何有助于合理化实际催化剂在工作条件下的行为的一些实例，探讨了模型系统与实际催化剂之间的关系。
