氧化铈表面活性氧物种的分子尺度调控

Tailoring the generation of active oxygen species on oxide surfaces, especially under mild conditions, is center to current catalysis research, partially owing to its potential application in the green chemistry of chemical conversion, emission control during cold start, oxygen reduction in fuel cell and lithium-air batteries. Paralleling its great importance is the tremendous difficulties confronting the oxidation catalysis research, in identifying the active sites on a complex oxide surface and understanding their role in O2 activation. Taking ceria, a renowned material for catalytic oxidation, as an example, previous spectroscopic studies have identified a series of active oxygen species on ceria, upon its contact with O2 at room temperature. While surface oxygen vacancies on ceria are generally expected as the sites for O2 activation, where and how these different oxygen species are generated remain unknown. Recent advances in the microscopic studies of ceria surfaces revealed a few types of oxygen vacancies at the ceria surface, which leads to the hypothesis that the series of active oxygen species could be generated by these different oxygen vacancies, respectively.Surface science studies, combing STM, IRAS and EPR, on ceria model surfaces will thus allow the answer to this hypothesis.Certainly,the bulk ceria is not active enough for the generation of most active oxygen species at around room temperature. However, understanding the nature of electron transfer between oxygen vacancies and O2 in generating different oxygen species, one could tune the electronic structure of ceria through nano- and interface- confinement effects, to enhance the electronic interaction with O2. Interfacial confinement is our recently developed strategy, that can drastically enhance the catalytic performance of an oxide.Due to the strong interaction between metal and oxides, oxide nanostructures can exhibit great structural flexibilities when supported on a metal surface. Low-valence active centers can thus be stabilized at the interface and the oxides can exhibit a series of novel structures not seen in the bulk phase. Interface-confined ceria, with the precise control of surface science approach, would thus allow the tailored generation of active oxygen species for selective oxidation at low temperature.

开发高效的低温氧化催化剂是当前催化研究的一个重点，这其中氧化铈是极具潜力的催化氧化材料，室温下即可与O2反应，形成一系列的表面氧物种。由于氧化铈表面结构的复杂性，对于这些氧物种的形成机理，至今未能有完善的理解。我们拟结合STM，IRAS和EPR等表征技术来研究氧化铈模型表面，考察氧化铈表面不同种类的氧空位是否与不同氧物种的形成存在对应关系；通过对不同氧物种的形成过程的认识，理解氧空位与O2之间的电子转移机制。当然，体相氧化铈的活性，不足以在室温条件下产生十分活泼的氧物种，我们可以通过纳米和界面限域效应来进一步调变氧化铈的电子结构，以增强其与O2的作用。由于氧化物和金属界面的强相互作用，负载的氧化物纳米结构具有很好的可调控性。低价态的活性中心可以在界面处得到稳定，而氧化物本身也可形成一系列迥异于体相的新奇结构。我们预期可通过对界面限域氧化铈体系的精确调控，实现低温下活性氧化物种的选择性生成。

开发高效的低温氧化催化剂是当前催化研究的一个重点，这其中以氧化铈为代表的氧化物纳米结构是极具潜力的催化氧化材料，可在温和条件下与O2反应，形成一系列的表面氧物种。由于氧化物表面结构的复杂性，对于这些氧物种的形成机理，至今未能有完善的理解。我们拟结合STM，SRPES等表征技术来研究氧化铈模型表面，考察氧化铈表面不同种类的氧空位是否与不同氧物种的形成存在对应关系；通过对不同氧物种的形成过程的认识，理解氧空位与O2之间的电子转移机制。当然，体相氧化铈的活性，不足以在室温条件下产生十分活泼的氧物种，我们可以通过纳米和界面限域效应来进一步调变氧化铈的电子结构，以增强其与O2的作用。本项目针对由于氧化物和金属界面的强相互作用，通过对负载氧化物纳米结构的调控，形成低价态的活性中心，并在界面处得到稳定，而氧化物本身也可形成一系列迥异于体相的新奇结构。我们通过对界面限域氧化物体系的精确调控，实现了低温下活性氧化物种的选择性生成，并进一步针对选择性氧化反应和纳米粒子在氧化反应中的动态结构和稳定性研究取得了一些进展。