EXAFS ESTIMATION OF THE CHANGES OF THE WS2 SLAB SIZE DURING THE USE IN A HDS RUN AND REGENERATION

A series of Ni-W/Al2O3-SiO2 catalysts with different Al2O3/SiO2 ratios were prepared and loaded in a commercial HDS unit for one year. The c atalytic properties of the freshly sulfided, spent and regenerated cat alysts were investigated by performing structural analysis and model t est reactions. The aggregation of WS2 slabs in the lateral direction i n the spent catalysts, which was observed by EXAFS and TEM, was a majo r cause of the catalyst deactivation. The addition of SiO2 into the ca talyst support was found to suppress the structual changes of the cata lyst. The lumps of WS2 were composed of several layers in the regenera ted catalysts and the WS2 slabs were smaller than those of the spent c atalysts. The hydrodesulfurization activities of the regenerated catal ysts were almost the same as those of the fresh catalysts. Therefore, the performance of the hydrotreating catalysts was found to be affecte d mainly by the structure of the active metals.