Atomic scale analysis of sterical effects in the adsorption of 4,6-dimethyldibenzothiophene on a CoMoS hydrotreating catalyst

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  • Signe Strange Grønborg
  • ,
  • Manuel Šarić, Technical University of Denmark, Denmark
  • Poul Georg Moses, Haldor Topsøe A/S, Denmark
  • Jan Rossmeisl, Copenhagen University, Denmark
  • Jeppe V. Lauritsen
The low catalytic hydrodesulfurization (HDS) activity toward sterically hindered sulfur-containing molecules is a main industrial challenge in order to obtain ultra-low sulfur diesel. In this study we report a combined Scanning Tunneling Microscopy (STM) and Density Functional Theory (DFT) investigation of the adsorption of the sterically hindered sulfur-containing molecule 4,6-dimethyldibenzothiophene (4,6-DMDBT) onto a hydrotreating model catalyst for the Co promoted MoS2 (CoMoS) phase. The molecular adsorption occurs exclusively on the Co-promoted S-edge, most predominantly in a precursor-like diffusive physisorption referred to as delocalized ππ-mode. 4,6-DMDBT adsorption directly in a S-edge sulfur vacancy is observed exclusively in S-edge corner vacancies in an adsorption configuration reflecting a σσ-coordination. STM movies reveal dynamic conversion between the σσ-mode and an on-top ππ-adsorption providing a link between different adsorption sites and hence between the hydrogenation and direct desulfurization pathways in HDS. The low overall direct desulfurization activity of 4,6-DMDBT and related molecules is consistent with the low occurrence of S-vacancies on CoMoS S-edges predicted under HDS conditions in this study.
Original languageEnglish
JournalJournal of Catalysis
Pages (from-to)121-128
Number of pages7
Publication statusPublished - Dec 2016

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