Title : Investigation of Zr promoted Cobalt based Fischer Tropsch catalyst at high syngas conversion
Abstract:
Fischer–Tropsch synthesis (FTS) is a route to produce liquid fuels from natural gas, coal and biomass. Ruthenium, iron and cobalt are most active metals for FTS. Cobalt preferentially produces more paraffinic hydrocarbons. Al2O3, TiO2 and SiO2 are currently used as supports for commercial cobalt catalysts. To facilitate the reduction of Co, which has strong interactions with Al2O3, researchers often add promoters such as Pd, Pt, Re, and Ru to the Cobalt catalysts. The cobalt based catalysts were prepared by a wet impregnation method. The catalysts were prepared in two steps: (step 1) Support of γ-alumina was stabilized by addition of Zr; (step 2) Co and Ru were deposited by wet impregnation to 25 nominal wt % and 0.2 wt % respectively. In Step 1, supports were impregnated with Zr using an aqueous Zircoium nitrate. The catalyst was dried at 120 oC then calcined at 400 ?C for 3 h. For steps 2, Co and Ru were added to the Zr-stabilized support by wet impregnation method using Cobalt nitrate (Co(NO3)2.6H2O (merck, purity> 97% )) and Ru(NO)(NO3)3 (ACROS ORGANICS, in diluted nitric acid 0.01 ml/ml) targeting 25 wt % and 0.2 wt % of cobalt and Ru loadings for two steps. The final catalysts dried at 120 ?C for 16 h and calcined at 400 ?C for 3 h. The effect of zirconium promoter over Co-Ru/γ-Al2O3 was investigated. The Co loading was 25 wt. % on the catalysts. XRD, BET , TEM , and H2-TPR techniques were utilized to assess the catalysts phase, structure, morphology, and reduction temperature. Catalytic performance of the catalysts were studied in a fixed bed reactor. The catalysts were activated in situ with hydrogen at 400 ?C for 16 h, then tested at the following conditions: T= 220 ?C, P= 25 bar, H2/CO= 2, GHSV= 2nl.h-1.gCat-1. Both the promoter and the reaction conditions influence the product selectivity. The product distribution of hydrocarbons can be described by the Anderson-Schulz-Flory (ASF) equation: mn=( 1-α) αn-1 with mn the mole fraction of a hydrocarbon with chain length n and the growth probability factor α independent of n. The Zr promoted catalyst exhibited a high catalytic activity and high selectivity to C5+ hydrocarbons in the FTS reaction.
