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

用原位荧光XAFS技术研究了Co-W和Ni-W硫化物催化剂中Co和Ni的局域结构。讨论了钴、镍的结构随反应气氛和温度的变化，以及添加络合剂对钴、镍硫化性能的影响。在没有络合剂的情况下，Co和Ni的硫化反应随着温度的升高而迅速进行，并在473K时基本完成。而含有氮三乙酸(NTA)的Co-W/Al_2O_3和Ni-W/Al_2O_3催化剂的Co和Ni物种在室温下几乎没有硫化。此外，XANES分析表明，即使在更高的温度下，NTA的存在也显著抑制了硫化速度。添加NTA的Co-W/Al_2O_3催化剂对噻吩加氢脱硫的催化活性明显高于添加NTA的Ni-W/Al_2O_3催化剂。XANES分析表明，添加NTA的Co-W催化剂中钴硫化物的生成受到明显的抑制。

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.