掺杂氧化铈基准单相透氧膜的微结构及性能研究

Single phase perovskite-type membranes and cobalt-containing dual phase oxygen permeable membranes were often employed for the conversion of light hydrocarbons or hydrogen production from water splitting. However, cobalt are easily deeply reduced, leading to the membrane failure, during water splitting. Ceria-based oxygen ion conductors exhibit electronic conductivity under reducing conditions, and thus can be used as oxygen permeable membrane reactors. In this project, small amount of cobalt oxide will be added into the ceria-based membrane to make the sintering process easier, thus forming quasi-single phase ceria-based oxygen permeable membrane. Here, the oxygen permeability of ceria-based membrane is expected to be improved by varying the type of the dopants and their content, and by decreasing the thickness of membrane. Water splitting will be coupled with partial oxidation of methane on the opposite sides of the above oxygen permeable membrane, and thus a continuous hydrogen flux on one side and synthesis gas on the other side of the membrane are expected. Considering the discontinuous distribution of cobalt-containing particles and the valence of Ce will only change from +4 to +3 without further deep reduction, the quasi-single phase membranes are expected to be stable under the above reducing conditions. It is believed that the planned research work on such kinds of quasi-single phase membranes will be highly valuable for the efficient conversion of light hydrocarbons.

钙钛矿单相膜以及含钴的双相透氧膜可用于低碳烷烃转化以及水分解制氢气。在水分解反应过程中，钴易被深度还原，导致膜的破裂。掺杂氧化铈基氧离子导体在还原性气氛也具有电子导电能力，可用作透氧膜反应器。为了改善膜材料的烧结性能，本项目中我们将向氧化铈基膜体系中引入少量氧化钴，形成掺杂氧化铈基准单相透氧膜。我们将重点考察氧化钴的引入对准单相膜的微结构、透氧能力及化学稳定性的影响。同时拟通过改变掺杂元素的类型、掺杂量以及膜的厚度等方法来提高准单相膜的透氧性能。将高温水分解和甲烷部分氧化反应耦合在上述准单相膜的两侧，由于氧化钴颗粒在膜体系中分布的不连续性，而且Ce 的化合价仅从+4 变为+3，但不会被进一步深度还原，该准单相膜可望呈现较高的化学稳定性。这样在膜的一侧可以连续得到氢气，而在另一侧可以得到合成气。相信此类准单相透氧膜方面的工作将为未来低碳烷烃的高效转化提供有力支持。

钴基钙钛矿型透氧膜可用于低碳烷烃转化及水分解反应，但钴易被深度还原导致膜破裂。本项目通过调变氧离子导体（Gd、Sm、Pr等掺杂的CeO2-δ）和电子导体（CoO、CuO及铁基钙钛矿）的种类和含量制备了一系列氧化铈基透氧膜，并对其微结构进行表征分析。借助干压法和流延成型法调控膜厚，并考察不同反应气氛下氧化铈基透氧膜的分离和还原稳定性能，发现降低电子导体相掺杂比例可以提高氧化铈基透氧膜的还原稳定性，低电子导体掺杂量的氧化铈基透氧膜表现出比常见的钙钛矿单相膜更好的还原稳定性。通过研究“H2O/CH4”、“N2O/CH4+CO2”、“CO2+H2O/CH4”、“air+H2O/CH4”反应体系，发现掺杂氧化铈基透氧膜在实际反应气氛中具有优异的稳定性，实现水分解制氢气生成速率达3 mL min-1 cm-2，甲烷部分氧化反应中CH4转化率和CO选择性均达90 %以上，并在实际操作条件下稳定运行数百小时，为提高透氧膜还原稳定性及在低碳烷烃转化中的应用提供了有力支持。