Podkolzin S.G.

MS/BS Thesis, State University of Oil & Gas, Moscow, Russia, 1988.

Joint project with Zelinsky’s Institute of Organic Chemistry, Russian Academy of Sciences.

Effects of additives on the stability and reactivity of sulfides on surfaces of petroleum hydrotreating catalysts

    A series of alumina-supported Co-Mo hydrotreating catalysts promoted with an alkali metal, Na or K, was prepared, characterized and tested in the thiophene desulfurization probe reaction.  In addition, kinetic data were collected on the rate of sulfur exchange between catalyst surface sulfides and H₂S by pretreating catalysts with ³⁵S and monitoring the isotope level of the catalytic surface and the formed hydrogen sulfide. 

    The formation of H₂S from surface sulfides, and not directly from the thiophene feed, was confirmed.  The amount of sulfur on the catalyst surface that could be hydrogenated to form H₂S and then be replaced by thiophene sulfur - the exchangeable surface sulfur - was about 4% of the total catalyst sulfur content for a 12 wt. % Mo on alumina catalyst.  The amount of the exchangeable sulfur increased to 40% for a Mo catalyst with 4 wt. % Co.  Addition of Na or K to Co-Mo catalysts further increased the exchangeable sulfur level to 45%.  Futhermore, catalysts with an alkali-metal promoter had higher stabilities.  The amount of the exchangeable sulfur, as determined with ³⁵S experiments, correlated well with the catalytic activity in hydrodesulfurization.  The tested alkali-Co-Mo samples had better activity and stability compared to commercial Mo catalysts for hydrotreating of heavy-oil fractions .

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