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

Abstract

The deactivation of a Co–Ru/Al 2O 3 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 N 2 at the reaction temperature, then the N 2-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.