Identification of the carbonaceous compounds present on a deactivated cobalt based Fischer–Trospch catalyst resistant to “rejuvenation treatment”

The deactivation of a Co–Ru/Al2O3 catalyst during a Fischer–Trospch process was examined under relevant industrial conditions, 220 °C and 2 MPa. The decline in CO conversion can result from several causes such as oxidation, sintering and carbon deposition. The aim of this work was to identify the carbon compounds deposited on the spent catalyst. At the end of the experiment, the catalyst was first stripped by N2 at the reaction temperature, then the N2-stripped sample was soxhlet-extracted with cyclohexane to recover the “light waxes” trapped in the catalyst pores. Then, the catalyst was dissolved in HF in order to remove the inorganic components and to recover the residual carbon called “coke”.Spent catalyst samples obtained at different points in time on-stream were analyzed using various techniques such as nitrogen adsorption, TPH-MS, TPO-MS and TPH-IR-MS. The coke was constituted of four kinds of carbonaceous compounds: atomic carbon, alcohols, carboxylic acids and polymeric carbon. Only the two last families were resistant to a rejuvenation treatment under hydrogen.

Graphical abstractGC–MS analysis of the coke species extracted by HF on the 21 days spent catalyst.Figure optionsDownload full-size imageDownload high-quality image (83 K)Download as PowerPoint slideHighlights► FT cobalt catalysts deactivate with the time on-stream. ► Stripped waxes, light waxes and coke are present on the catalytic bed. ► Carbon, n-alcohols, polymeric carbon, carboxylic acids compose the coke. ► Polymeric carbon and carboxylic acids were resistant towards the rejuvenation.