氧存在下钙钛矿LaCoO3硫化过程的XPS研究

 采用XPS，XRD和TEM对含氧气氛下钙钛矿LaCoO3硫化活化过程中不同阶段的催化剂进行了表征分析．在硫化初期，经SO2预中毒后，吸附氧种不存在，Co2p3／2结合能发生明显的位移，La3d的XPS双峰变得不明显，同时出现不稳态的S4＋物种，表明催化剂LaCoO3被SO2的强吸附所覆盖；催化剂LaCoO3仍为钙钛结构并没有新的物相产生，SO2中毒仅在催化剂表面进行．在进一步的硫化活化过程中，出现吸附氧物种，Co出现三种价态，分别对应于LaCoO3，Co3O4和CoSO4，La3d的XPS双峰变得特别明显，同时催化剂表面出现S2－物种和S6＋物种．可以认为，在含氧气氛下硫化LaCoO3的过程中，SO2预中毒为进一步硫化提供硫物种，吸附氧物种保证硫化过程中钙钛矿结构不会被完全破坏．

XPS Study on Sulfurization Process of LaCoO3 in the Presence of Oxygen

It was found in our previous study that the process of activation sulfurization of LaCoO 3 plays a necessary role in the catalytic reduction of SO 2 with CO to element S in the presence of oxygen. In order to explain the phenomenon, the process of activation sulfurization of LaCoO 3 in the presence of oxygen was studied by XPS, XRD and TEM methods. The valence variety on LaCoO 3 surface in various processes of activation sulfurization was investigated. When LaCoO 3 was pre poisoned by SO 2, the adsorbed oxygen on its surface was absence, the chemical shift of binding energy of Co 2 p 3/2 was more than 1.0 eV, the La 3 d double peak turned unobvious, and at the same time the S 4+ appeared on the surface, indicating that the perovskite was overlapped by the strongly adsorbed SO 2 species. The results of XRD and TEM showed that after poisoned by SO 2 no new phase appeared on the surface of perovskite LaCoO 3. However, after activation sulfurization the surface adsorbed oxygen reappeared, corresponding to LaCoO 3, Co 3O 4 and CoSO 4, Co had three valence states, La 3 d double peak got clarity, S 2- and S 6+ appeared on the surface of LaCoO 3. During the activation sulfurization of LaCoO 3 in the presence of oxygen, the SO 2 poisoning on perovskite supplied S 2-species to sulfurize the perovskite LaCoO 3, and the surface adsorption oxygen made perovskite structure stable.