含US-SSY分子筛的Ni-W-γ-Al2O3体系的EXAFS研究

运用EXAFS技术分别对含有自冷和急冷US-SSY分子筛的Ni－W－γ－Al_2O_3样品中的w的LⅢ吸收边和Ni的K吸收边进行了结构分析。结果表明分子筛超稳化后的冷却速率对样品中原子的局域结构有影响，进而影响了样品的催化活性。急冷样品中W的分散度比自冷样品差，其八面体结构含量较高，并有钨钼氧原子簇产生。但急冷催化样品中Ni具有较高的分散度，Ni-W间距小，较易形成“Ni－O－W”物种。由于八面体结构中的氧在加氢脱硫反应中较易被硫取代，且“Ni-O-W”物种是HDS反应的活性前驱体，导致急冷样品具有较高的HDS活性。加快分子筛超稳化后的冷却速率可提高催化剂样品的活性。

EXAFS Studies of Ni-W Hydrotreating Catalyst Based on US-SSY Zeolite

The Ni-W hydrotreated catalyst based on US-SSY zeolite was studied by extended X-ray absorption fine structure(EXAFS) .The results obtained at Ni 1s edge and W 2p3/2 edge showed that the local structures around Ni and W atoms, and the hydrodesulphurization (HDS) activity can be significantly affected by the cooling rate. In fast cooling catalyst. octahedral structure was move abundant, but the dispersion of W was not so good as that in self cooling catalyst.W-O-Mo clusters were found to be only associated with fast cooling catalyst, which contains better dispersed Ni, with smaller atomic distance between Ni and W atoms. It was found also that "Ni-O-W" species can be easily formed. Sinceoxygenion in a W - O bond in octahedral structure can be easily substituted by sulfur in HDS reaction and "Ni-O-W" species are the catalst precursors of HDS, fast cooled catalyst may enhanced HDS activity.