Abstract
AbstractThe changes, which take place in the structural and catalytic properties of Co‐Mo/Al2O3 catalysts sulfided at different temperatures, have been elucidated by means of high resolution electron microscopy (HREM), ir, XRD, and chemisorption of oxygen. It was observed that high temperature sulfiding induces a growth in the Co‐Mo‐S crystals which are MoS2‐like with Co occupying edge positions. For all the catalysts, Co‐Mo‐S was found to be the most important feature in determining the HDS activity and it was found that the changes, which occur with the HDS activity, can be explained in terms of the changes in the total MoS2 edge area and its Co coverage. When saturation edge coverage is exceeded, segregation of excess Co in the form of Co9S8 takes place. Differences in the hydrogenation activity can be explained in terms of variations in the relative number of promoted vs. unpromoted MoS2 edge sites. Upon increasing the sulfiding temperature, the nature of the Co‐Mo‐S structure changes from a low temperature form (Type I Co‐Mo‐S) to a high temperature form (Type II Co‐Mo‐S). It is suggested that support interactions are less important for Type II Co‐Mo‐S than for Type I.
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