A Hybrid Reduction-Impregnation Method in Preparation of Co-Ru/gamma-Al2O3 Catalyst for Fischer-Tropsch Synthesis

摘要

Three cobalt catalysts (Co) promoted by ruthenium supported on gamma-Al2O3 were synthesized by incipient wetness co-impregnation (I/I), successive reduction (R/R), and a novel hybrid reduction-impregnation (R/I) methods. The Co loading in all of the present catalysts was 15.0 wt% and that of Ru was 0.15 wt%. To study the influence of the preparation methods on activity and selectivity of the Fischer-Tropsch synthesis, we used the prepared catalysts in a fixed-bed reactor. The different characteristic analysis tools such as X-ray diffraction, Transmission electron microscopy, Hydrogen temperature-programmed reduction, Brunauer-Emmett-Teller, Inductive Coupled Plasma and Energy-dispersive X-ray were carried out to determine the properties of the present prepared catalysts. The TPR peaks for Coai...Ru/Al2O3(R/I) catalyst were presented significantly at lower temperatures than those obtained for the Coai...Ru/Al2O3 (I/I) and Coai...Ru/Al2O3 (R/R) catalysts. The average sizes of the cobalt oxide particle were calculated as 7.9, 17.2, and 37.3 nm for Coai...Ru/Al2O3/R/R, Coai...Ru/Al2O3 (R/I), and Coai...Ru/Al2O3 (I/I), respectively, which are nearly consistent with those sizes obtained by TEM images. Using Coai...Ru/Al2O3(R/I), the enhancement in CO conversion, C5+ selectivity, and chain-growth probability were 30, 18, 12.5%, respectively, in compared to those obtained by Coai...Ru/Al2O3 (I/I) whereas the Coai...Ru/Al2O3 (R/R) catalyst did not highly improve the FT performance with respect to Coai...Ru/Al2O3 (I/I). Moreover, the highest CO conversion, C5+ selectivity, chain-growth probability factor and the lowest C-1 selectivity belonged to the hybrid reduction-impregnation method. The effects of temperature (T = 210-230 A degrees C) and pressure (P = 10-20 bar) were thoroughly investigated while H-2/CO ratio and GHSV were kept 2 and 1800 per hour, respectively. Using the reaction yield of C5+ as a criterion, the Coai...Ru/Al2O3(R/I) catalyst was selected to be the most productive catalyst at the optimum operating conditions 230 A degrees C and 10 bars.