Correlation between Fischer-Tropsch catalytic activity and composition of catalysts

Abstract

This paper presents the synthesis and characterization of monometallic and bimetallic cobalt and iron nanoparticles supported on alumina. The catalysts were prepared by a wet impregnation method. Samples were characterized using temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), CO-chemisorption, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM-EDX) and N2-adsorption analysis. Fischer-Tropsch synthesis (FTS) was carried out in a fixed-bed microreactor at 543 K and 1 atm, with H2/CO = 2 v/v and space velocity, SV = 12L/g.h. The physicochemical properties and the FTS activity of the bimetallic catalysts were analyzed and compared with those of monometallic cobalt and iron catalysts at similar operating conditions.H2-TPR analysis of cobalt catalyst indicated three temperature regions at 506°C (low), 650°C (medium) and 731°C (high). The incorporation of iron up to 30% into cobalt catalysts increased the reduction, CO chemisorption and number of cobalt active sites of the catalyst while an opposite trend was observed for the iron-riched bimetallic catalysts. The CO conversion was 6.3% and 4.6%, over the monometallic cobalt and iron catalysts, respectively. Bimetallic catalysts enhanced the CO conversion. Amongst the catalysts studied, bimetallic catalyst with the composition of 70Co30Fe showed the highest CO conversion (8.1%) while exhibiting the same product selectivity as that of monometallic Co catalyst. Monometallic iron catalyst showed the lowest selectivity for C5+ hydrocarbons (1.6%).

Effect of Ce and Co Addition to Fe/Al2O3 for Catalytic Methane Decomposition

“…The monometallic profile of 30%Co/Al2O3 has shown two peaks between 260 and 400 °C and between 410 and 750 °C. The TPR results have shown an interference between peaks observed for 30%Fe/Al2O3 and 30% Co/Al2O3 [21,22]. For mixed catalyst, 30%Fe-X%Co/Al2O3 catalyst profiles demonstrated a peak between 370 and 390 °C, which is attributed to the reduction of Fe2O3 to Fe3O4; while the broad signal observed between 500 °C and 730 °C represents a dual reduction mechanism starting with Co3O4 to Co slightly above 500 °C and Fe3O4 to Fe above 600 °C [13,[20][21][22].…”

“…The H2-TPR analysis was performed over 30%Fe/Al2O3 catalyst as a reference profile and over mixed catalysts (30%Fe-X%Ce/Al2O3 and 30%Fe-X%Co/Al2O3). As shown in Figure 1, monometallic 30%Fe/Al2O3 catalyst showed two peaks at 420 °C and a broad signal with a peak around 680 °C corresponding to conversion of Fe2O3 to Fe3O4 and reduction of Fe3O4 to Fe, respectively [13,[20][21][22]. The monometallic profile of 30%Co/Al2O3 has shown two peaks between 260 and 400 °C and between 410 and 750 °C.…”

“…Peaks at 2θ values of 28°, 43°, and 57° are corresponding to that of Co3O4. While 44° and 66° peaks are corresponding to Al2O3 [21,22]. For 30%Fe-X%Ce/Al2O3 catalysts, crystal phases of Fe2O3, Al2O3, and CeO2 are detected as shown in Figure 4.…”

“…For mixed catalyst, 30%Fe-X%Co/Al2O3 catalyst profiles demonstrated a peak between 370 and 390 °C, which is attributed to the reduction of Fe2O3 to Fe3O4; while the broad signal observed between 500 °C and 730 °C represents a dual reduction mechanism starting with Co3O4 to Co slightly above 500 °C and Fe3O4 to Fe above 600 °C [13,[20][21][22]. The simultaneous reduction of Fe3O4 and Co3O4 indicates the possibility of an interaction between Fe and Co, as confirmed by the hydrogen chemisorption [13,15,21,22]. One can note that the change in the bimetallic catalyst composition does not have a significant impact on the redox behavior of the catalyst, which may indicate the lack of formation of chemical compounds between Fe and Co particles.…”

Carbon Spheres Prepared by Hydrothermal Synthesis—A Support for Bimetallic Iron Cobalt Fischer–Tropsch Catalysts

“…[47,48] Other alloys that have been reported on Fe-Co systemsi nclude Fe 2 Co, Co 7 Fe 3 and Co/Fe supported on CaCO 3 ,S iO 2 and TiO 2 ,r espectively. [11,[49][50][51] It appearst hat the nature of the support materialu sed could influence the exact structure of the resultant alloy.T ot he best of our knowledge, there have been no literature reports on the in situ characterisation of Fe-Co systems supportedo nc arbons. Studies have been limitedt ot he PXRD characterisation of samples that were reduced ex situ at elevated temperatures.…”