Cu-Promoted Fe-Based Catalyst for Biomass-Derived Synthesis Gas for the Fischer-Tropsch Synthesis
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Four alumina supported iron-based catalysts were prepared by incipient wetness impregnation. The Fe loading was kept constant at 15 wt.%, and the Cu loading was varied between 0-5 wt.. The catalyst samples were characterized using CO chemisorption, adsorption of N2, temperature programmed reduction (TPR) in H2 and X-ray diffraction. The Fischer-Tropsch synthesis (FTS) was carried out using a fixed bed reactor pressurized to 20 bar(g) at 210, 230, 250 and 280 C. Increasing Cu loadings resulted in increasing metal dispersion, and decreasing surface area and pore size. Addition of Cu promoted the reduction of the catalyst in H2 The X-ray diffraction revealed that the iron oxide was reduced from Fe2O3 to Fe3O4 and metallic Fe during reaction. The Fischer-Tropsch synthesis display an increased CO conversion by addition of Cu to the catalysts. The catalyst sample with Cu loading of 5 wt.% yielded the highest CO conversion at lower temperatures, 210 and 230 C, at 43% and 50%, respectively. At higher temperatures the CO conversion decreased because of the reverse water gas shift reaction. At higher temperatures the catalyst with 2 wt.% Cu yields the highest CO conversion. The catalyst sample without addition of Cu appear to be more active than the catalyst with copper loadings of 0.6 and 2 wt.%, but was exposed to deactivation at higher temperatures. Due to strong interactions with the alumina support the carburization of the catalysts was suppressed and the adsorption of H2 enhanced, producing light hydrocarbons. The addition of Cu further enhanced the adsorption of H2 yielding a low olefin/paraffin ratio.