Abstract
Highly dispersed 15.0 wt% cobalt catalysts were prepared on γ-Al2O3, carbon nanotubes (CNTs), and graphene nanosheet (GNS) using chemical vapor deposition (CVD) procedure. The physico-chemical properties of the catalysts were studied by inductively coupled plasma (ICP), Brunauer–Emmett–Teller (BET), X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), and temperature-programmed reduction (TPR) techniques, and the Fischer–Tropsch synthesis (FTS) performance of the catalysts was assessed at 220 °C, 18 bar, H2/CO = 2 and feed flow rate of 45 ml/min g cat. Based on BET results, Co/GNS catalyst provided highest surface area in comparison to the other catalysts. XRD and FESEM results revealed that CVD method prepared smaller particles on GNS compared to the other supports and resulted in the most dispersed metal particles on GNS according to H2-chemisorption results. The performance of Co/Al2O3 catalyst prepared by CVD method was compared with conventional 15 wt% Co/Al2O3 catalyst prepared by impregnation method. The Co/Al2O3 catalyst prepared with CVD method showed 5.3% higher %CO conversion and 2.1% lower C5+ selectivity as compared with the Co/Al2O3 catalysts prepared by impregnation method. Among three catalysts prepared by CVD, Co/GNS showed higher %CO conversion of 78.4% and C5+ selectivity of 70.3%. Co/γ-Al2O3 catalyst showed higher stability.
Highlights
Fischer–Tropsch synthesis (FTS) is a major process in conversion of gas-to-liquids, coal-to-liquids, and biomass-toliquids
Cobalt catalysts are more expensive than iron catalysts, but they are resistant to deactivation
The distribution of cobalt ions on the surface of the support after impregnation is affected by some electrostatic interactions and van der Waals interactions that occur between the nanoparticles and results in the complex particle dynamics manifesting in deposition patterns on the support material [14]
Summary
Fischer–Tropsch synthesis (FTS) is a major process in conversion of gas-to-liquids, coal-to-liquids, and biomass-toliquids. The concentration, nature, and distribution of hydroxyl groups play an important role in the genesis of the dispersion of supported metal Porous supports such as silica, alumina, and titanium have different points of zero charges, and should be pretreatment before use [15]. CVD has chemical reactions of gaseous reactants on the vicinity of a heated substrate surface This method can provide a nanostructured and functionally coated materials with a special structure to use in different areas [19]. The advantage of this procedure is because of the uniform distribution of cobalt nanoparticles on catalyst support and possibility of a narrow distribution for cobalt particle size. Use of different types of cobalt materials could be explained by their low melting point and high vapor pressures [20]
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