Applications and mechanistic understanding of rare earth oxides in catalysis

稀土氧化物由于其良好的催化性能，特别是在完全氧化和部分氧化反应中得到了广泛的应用。然而，尽管有这种潜力，迄今为止只有铈得到了详细的研究。我们提出了一个合作项目，以扩大范围，并遵循双重方法，通过制备选择性REOs作为在特高压条件下研究的明确定义的薄膜和在实际反应条件下催化研究的纳米结构材料。作为可还原的氧化物，REOs表现出可变的价态，因此在氧化物晶格内具有高氧迁移率的化学计量学。这些特性使它们能够通过所谓的Mars van Krevelen机制积极参与表面氧化还原反应，即晶格氧与吸附的反应物交换。作为化学性质大不相同的例子，我们将选择Tb（氧化态：+3，+4）和Sm（氧化态：+2，+3）。以甲烷氧化偶联反应（OCM）为测试反应，我们的目标是基本了解REOs对部分氧化反应和完全氧化反应的选择性，并探索通过碱掺杂和纳米级尺寸效应调节REOs催化选择性的方法。

Rare earth oxides (REOs) have attracted considerable attention due to their favorable properties for several catalytic applications, in particular complete and partial oxidation reactions. In spite of this potential, however, only ceria has been studied in great detail so far. We propose a collaborative project to broaden the scope and follow a twofold approach by preparing selected REOs as both well-defined thin films for studies under UHV conditions and nanostructured materials for catalytic studies under practical reaction conditions. As reducible oxides, REOs exhibit variable valence states and thus stoichiometries combined with high oxygen mobility within the oxide lattice. These properties enable them to actively participate in surface redox reactions through the so-called Mars van Krevelen mechanism whereby lattice oxygen is exchanged with adsorbed reactants. As examples with a largely different chemistry, Tb (oxidation states: +3, +4) and Sm (oxidation states: +2, +3) will be chosen. Taking the oxidative coupling of methane (OCM) as a test reaction, we are aiming at a basic understanding of the selectivity of REOs toward partial vs. complete oxidation reactions, and an exploration of methods for tuning the catalytic selectivity of REOs through alkali-doping and nanoscale size effects.