Deactivation behavior of ruthenium promoted Co/-γ-Al2O3 catalysts in Fischer-Tropsch synthesis

Detailed activity study and the deactivation of Ru-Co/-gamma-Al2O3 catalyst for Fischer-Tropsch (FT) synthesis over 1000 h was investigated considering different deactivation mechanisms. Morphology changes of the catalyst during FT synthesis were studied using XRD, TPR, BET, ICP, carbon determination, H-2 chemisorption and re-oxidation techniques. When the P-H2O/(P-H2 + P-CO) in the reactor is above 0.75 the deactivation rate is not dependent on the number of the catalyst active sites and is zero order to CO conversion. In this case the main deactivation mechanisms are: cobalt re-oxidation, metal support interactions and aluminates formation. The deactivation of Ru-Co/-gamma-Al2O3 is related to cobalt cluster size. At lower amounts of P-H2O/(P-H2 + P-CO) deactivation can be simulated with a power law expression with a power order of 39.7 and the main deactivation is due to sintering. Regeneration of catalyst at 275 degrees C recovered the catalyst activity by 69.9% of total activity loss due to the reduction of oxidized cobalts. Catalyst regeneration at 400 degrees C recovered the activity by 21.9% of total activity loss due to the reduction of refractory forms of oxidized cobalt generated by cobalt-alumina interactions. 7.2% of total activity loss is irreversible and can be assigned to aluminates formation, sintering and coke deposition. (C) 2008 Elsevier B.V. All rights reserved.