from first principles PP-I-1

OP-III-12Different Carbon Species and Deactivation of Alumina Supported CobaltFischer-Tropsch Catalysts in Slurry ReactorDiehl F. 1 , Lecocq V. 1 , Griboval-Constant A. 2 , Khodakov A.Y. 2 , Peña D.A. 21 IFP Energies nouvelles, Rond-point de l'échangeur de Solaize, BP 3, 69360 Solaize, France2 Unité de Catalyse et de Chimie du solide, UMR CNRS 8181, Université Lille1-ENSCL-ECLille, Bâtiment C3, Cité scientifique, 59655 Villeneuve d’Ascq, Francediego-alexander.pena@etudiant.univ-lille1.frSupported cobalt catalysts are generally preferred for synthesis of clean fuels from natural gas,coal or biomass via Fischer-Tropsch (FT) synthesis due to their high activity and selectivity tolong-chain linear paraffins. Unfortunately, the catalyst activity decreases with time-on-stream.Cobalt catalyst deactivation appears to be a combination of several phenomena such as: surfacereconstruction, sintering, attrition and carbon deposition. Carbon deposition seems to be one ofthe major deactivation mechnisms especially in long term operations [1]. Our work focuses on theidentification and characterization of carbon species in cobalt catalyst, which form during FTreaction in a slurry reactor under different operating conditions and their role in catalystdeactivation. A 15 wt% Co supported catalyst on alumina carrier was prepared by incipientwetness impregnation with cobalt nitrate, then calcined and reduced. The catalytic performancewas evaluated in a CSTR slurry reactor of 100 cm 3 at 20 bar, at 220°C and stirring rate of 1000rpm with H 2 /CO ratios adjusted between 1-3 and different syngas velocities (GHSV). Theduration of catalytic tests was beyond 2-3 weeks. Carbon species and catalyst structure in waxcoatedcatalysts and after dewaxing were investigated using a wide range of techniques: XRD,TEM/SEM, XPS, TPH/TPR, XANES/EXAFS, TOF-SIMS. Cobalt oxidation was insignificantduring the catalytic runs, while HAADF-TEM showed limited cobalt sintering. Temperatureprogrammed hydrogenation coupled with mass spectrometry (TPH-MS) showed the presence ofthree types of carbonaceous species. XPS showed that the nature of the resilient carbons could be:(i) polymeric carbon, (ii) long chain hydrocarbon products remaining after wax extraction. Thetime of flight secondary ion mass spectrometry (TOF-SIMS) pointed out the presence of severalhydrocarbon species probably related with remaining wax, polymeric carbon and cobalt carbides.The concentration of these species correlates with the deactivation rate and is a function of reactoroperating conditions.References:[1] D.J. Moodley, J. van de Loosdrecht, A.M. Saib, M.J. Overett, A.K. Datye, J.W. Niemantsverdriet,Appl. Catal A : General 354 (2009) 102–110.55