Recent scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations have shed light on the atomic-scale structure of both Ni-Mo-S and Co-Mo-S catalysts, on the origin of high-activity type II sites and on the detailed molecular reactions taking place.  This has provided new opportunities for understanding and controlling the support interactions of the type II sites, the sensitivity to poisoning by nitrogen compounds and the detailed molecular reactions, which take place at the surface of the active phases.  These advances and the importance of the recently discovered metallic brim sites, which play a significant role especially for hydrogenation reactions, will be discussed.  The brim sites and the tendency to form vacancies are seen to differ for types I and II Co�Mo�S catalysts. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) studies show that the high activity type II structures may be present as single sulphide sheets.  Thus, stacking is not an essential feature of type II catalysts. Hydrocracking catalysts are strongly dependent on the hydrogenation efficiency of either Ni-W-S or Ni-Mo-S, and recent tests have shown that optimizing the sulphidation may significantly affect the performance. A deep understanding of the factors governing the removal of the most refractive compounds in diesel fuels is crucial to select the best catalyst for a given hydrotreater or hydrocracker.  Furthermore, a detailed understanding of catalyst preparation may lead to optimum catalytic activities.

Fundamental understanding of the role of reaction pathways and support interactions in hydrotreating and hydrocracking

242nd National Meeting (2011)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.