Applications and mechanistic understanding of rare earth oxides in catalysis

稀土氧化物(REO)因其良好的催化性能而备受关注，特别是在完全和部分氧化反应中的应用。然而，尽管有这种潜力，到目前为止，只有CeO2被非常详细地研究过。我们提出了一个合作项目，以扩大范围并遵循双重方法，通过制备精选的稀土氧化物作为在超高真空条件下研究的明确薄膜和用于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，REO具有不同的价态，因此其化学计量比与氧化物晶格中的高氧迁移率相结合。这些性质使它们能够通过所谓的火星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。作为具有很大不同化学的例子，将选择Tb(氧化态：3，4)和Sm(氧化态：2，3)。以甲烷氧化偶联(OCM)反应为例，我们旨在对REO对部分氧化反应和完全氧化反应的选择性有一个基本的了解，并探索通过碱掺杂和纳米尺度效应来调节REO的催化选择性的方法。

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.