Local Structure Analysis of Hydrodesulfurization Catalyst under reaction conditions by mean of In situ Fluorescence XAFS Technique

采用原位荧光XAFS技术研究了Co- w和Ni- w硫化催化剂中Co和Ni的局部结构。讨论了Co和Ni的结构随反应气氛和温度的变化以及加入螯合剂对Co和Ni可硫化性的影响。在没有螯合剂的情况下，随着温度的升高，Co和Ni的硫化迅速进行，在473K时几乎完成。另一方面，Co- w /Al_2O_3催化剂和Ni- w /Al_2O_3催化剂的Co和Ni在室温下几乎没有硫化。此外，XANES分析显示，即使在较高的温度下，NTA的存在也显著抑制了硫化速率。与Ni-W/Al_2O_3相比，添加NTA能显著提高Co-W/Al_2O_3对噻吩加氢脱硫的催化活性。XANES分析表明，在添加了nta的Co- w催化剂中，大量Co硫化物的形成被显著抑制。

The local structures of Co and Ni in Co-W and Ni-W sulfide catalysts are studied by means of an in situ fluorescence XAFS technique. The structural changes of Co and Ni with the reaction atmosphere and temperature and the effects of the addition of a chelating agent on the sulfidability of Co and Ni are discussed. In the absence of a chelating agent, sulfidation of Co and Ni rapidly proceeded with increasing temperature and almost completed at 473K. On the other hand, the Co and Ni species of Co-W/Al_2O_3 and Ni-W/Al_2O_3 catalysts with nitrilotriacetic acid (NTA) were scarcely sulfided at room temperature. Furthermore, XANES analysis revealed that the rate of sulfidation was significantly suppressed in the presence of NTA even at a higher temperature. It was also found that the catalytic activity of Co-W/Al_2O_3 for thiophene hydrodesulfurization was improved more significantly by the addition of NTA than that of Ni-W/Al_2O_3. It is demonstrated from the XANES analysis that the formation of bulk Co sulfide species is considerably suppressed in the NTA-added Co-W catalyst.