Towards Sustainable Fuels from Fischer-Tropsch Synthesis (original) (raw)
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The objective of this research is to find an optimal ratio of rare earth elements (RE), lanthanum (La) and cerium (Ce), as promoters of Co-based Fischer–Tropsch synthesis (FTS) catalysts to achieve maximal diesel yield. These synthesized rare-earth promoted catalysts were characterized with Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD) and hydrogen temperature programmed reduction (H 2-TPR). The effects of La/Ce molar ratio on the FTS performance of silica gel supported cobalt based catalysts were investigated in a fixed bed reactor at temperatures of 220 and 240 • C. The evaluation tests show that the catalysts promoted by composited rare-earth (CRE) with appropriate molar ratio La to Co have better FTS performance than unpromoted and individual rare-earth (IRE) promoted catalysts. The results show that the CRE promoted FTS catalysts are promising. The CO conversion is increased significantly and the selectivity for methane and C 2 –C 4 is decreased while the selectivity for long chain hydrocarbons is greatly increased (C 5 + increased from 70.36 to 80.25% at 220 • C and from 69.94 to 78.02% at 240 • C, respectively). Among all CRE modified catalysts, based on the result of distribution of C 12 –C 18 (weight% of hydrocarbons), Co-1La2Ce/S.G (n RE: n Co = 0.1 and n La: n Ce = 1:2) is proven as a highly efficient catalyst for production of diesel rich synthetic oil from coal-derived syngas.
2015
Biomass gasification as a thermochemical treatment method is typically used for heat and power production. Instead of burning the producer gas, it can be converted to added-value products, i.e to fuels and chemicals. One such conversion is the catalytic Fischer-Tropsch synthesis (FTS) which converts synthesis gas to a chain of aliphatic hydrocarbons (FT diesel) as studied in this thesis. This requires, however, proper cleaning steps of producer gas, such as the removal of tar compounds and other impurities. These cleaning steps are not considered in this thesis. The first goal of the thesis was to determine the tar content in the producer gas from a small scale biomass gasifier. This subject is discussed in Paper I. The second and main goal of the thesis was the preparation and characterization of cobalt (or iron) catalysts for catalytic conversion of a gas mixture close to the synthesis as discussed in Papers II-V. The overall aim of the second part was to study the effects of promoters on the reducibility of cobalt and the effects of different calcination conditions on the degree of reduction and size of the metallic cobalt particles. In this later part different catalytic supports were used. According to the results of the thesis, naphthalene and toluene were the main tar compounds in the producer gas representing almost 80 % of the GC detected tar compounds. Only traces of polycyclic aromatic compounds were detected and no phenolic compounds were found in the gas. Further, a number of supported heterogeneous catalysts for FTS using cobalt (Co) or in some cases iron (Fe) as the active metal were prepared and characterized. These catalysts were supported on alumina (Al 2 O 3), titanium dioxide (TiO 2) or silicon carbide (SiC). Catalysts were promoted with Ru, Re or Rh in the concentrations of 0, 0.2, 0.5, and 1.0 mass-%. Several characterization methods (such as H 2-TPR, catalytic activity measurements, N 2 physisorption, CO chemisorption, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD)) were used to find answers to the behaviour of these catalysts under selected conditions and in the model reaction of FTS. Based on the results, there are significant differences in the characteristics of the catalysts, the differences are dependent of the supports used, promoters added and calcination conditions used. The properties of the support, especially the pore size distribution will effect the distribution of products formed in the Fischer-Tropsch synthesis. Addition of promoters and variatons in calcination conditions will effect the dispersion and the particle size of the active metal.
Insight into the Physicochemical Properties of Co-Based Catalysts in Fischer–Tropsch Synthesis
Reactions
The effect of the different supports and catalyst-reducing agents on the Fischer–Tropsch (FT) reaction was investigated. The large surface area SiO2 support with a smaller pore volume deposited fine, evenly distributed Co3O4. Cubic-shaped Co3O4 appeared in clusters on the TiO2 support, whereas Co3O4 existed as single large particles on the Al2O3 support. The activity data obtained were discussed in terms of cluster size, particle size, particle shape, and mass transport limitations. The SiO2-supported catalysts showed a higher activity for the formation of paraffinic products when reduced in H2 at 250 °C. This is attributed to the formation of the CoO-Co active bond, which enhanced the activation of CO and the hydrogenation reactions. A higher activity was observed for the TiO2-supported catalyst at a higher reduction temperature (350 °C) when the mass of Co metal was higher. It afforded more paraffinic products due to enhanced secondary hydrogenation of olefins at higher reaction r...
Studies in Surface Science and Catalysis - STUD SURF SCI CATAL, 2007
Several iron-based catalysts supported on different oxide carriers (CeO2, MnO, ZnO) were synthesized by the combustion route and probed in the Fischer-Tropsch synthesis reaction in the range 250-300°C and at 10-20 bar total pressure, using a PF-reactor and various COx reaction mixtures (H2/CO=2 or H2/CO2=3 or (CO+CO2)/H2=2). The prepared catalysts feature a catalytic performance superior to that of commercial FT catalysts and suitable for industrial application as a very high activity (100-60 of COx conversion), selectivity (low methane and high long-chain product selectivity; ASF parameter close to 0.9) and long lifetime (500 h).
Journal of Catalysis, 2002
Iron-based catalysts were prepared by using promoters (K, Ru, Cu) and synthesis and activation protocols that inhibit sintering of oxide precursors and favor the nucleation of small Fe carbide crystallites. The effects of promoters on reduction/carburization behavior, on Fischer-Tropsch synthesis (FTS) rates, and on the number of CO binding sites formed during reaction were examined by combining steady state and transient rate measurements, titration of active sites, and X-ray absorption spectroscopy. K, Ru, and Cu promoters increased reduction/carburization rates of Fe-Zn oxide precursors, steady-state FTS rates, and the number of CO binding sites present after activation and FTS. These promoters increased the number of active sites formed during activation by favoring the nucleation of smaller Fe 3 O 4 and FeC x domains as Fe 2 O 3 precursors were transformed into active catalysts during initial contact of oxide precursors with synthesis gas. These smaller crystallites, in turn, provide higher surface areas, a larger number of CO binding sites, shorter distances for lattice oxygen diffusion during carburization, and higher steady state FTS rates. The use of surface-active alcohols during drying and thermal treatment of oxide precursors also led to higher active site densities and FTS rates; these methods minimized sintering of oxide precursors during these thermal treatments. Turnover rates on Fe-based catalysts were about three times lower than on Co-based catalysts, at conditions typical used for the latter (473 K, 2.0 MPa). Hydrocarbon synthesis rates (per catalyst mass or volume) on Fe-Zn-Cu-K catalysts prepared by the methods described here were similar to those on representative Co-based catalysts at these conditions. Fe-Zn-Cu-K catalysts gave much lower CH 4 selectivities than Co-based catalysts. Fe-based catalysts also showed much weaker effects of temperature and of synthesis gas composition on CH 4 and C 5+ selectivities. CO 2 selectivities were lower than on previous Fe-based catalysts, predominately because of the lower reaction temperatures made possible by the high active site densities attained on the promoted Fe-Zn catalysts reported in this study.
Industrial & Engineering Chemistry Research, 2019
Fischer-Tropsch (FT) synthesis is an important reaction for the alternative production of high-quality liquid fuels, which promote sustainable development by enabling economical decarbonization. The one-stage FT process involves both hydrocarbon growth and hydrocracking/isomerization in a single step and is more energy-and cost-efficient than the two-stage process. Bifunctional catalysts, composed of acid and metal sites, are needed in order to achieve one-step synthesis. In this review, we will discuss on the state of the art concerning the use of bifunctional catalysts for the one-stage FT process, focusing on the effect of metal and acid sites on the catalytic performance. Several supports with potential utility for the one-stage FT process were analyzed, including zeolites, clays, alumina, silica, aluminosilicates and carbons, and the advantages and disadvantages of each were evaluated.
Catalysis Communications, 2011
The effect of CO 2 was studied for cobalt and iron Fischer-Tropsch (FT) synthesis. CO 2 behaves differently in the presence of CO over cobalt and iron catalysts in terms of hydrogenation. A systematic increase of the CO 2 mole fraction of carbon in the feed gas mixture alters the product distribution dramatically for cobalt FT synthesis with CO 2 behaving like an inert gas at higher partial pressure of CO. With cobalt, CO appears to compete with CO 2 for adsorption. Using an iron FT catalyst, hydrogenation of CO 2 was effected due to the presence of the reverse water-gas shift activity of the catalyst which converts CO 2 to hydrocarbons through the formation of CO. Unlike the cobalt catalyst, the product distribution was only slightly altered with increasing CO 2 content in the feed gas mixture to the iron catalyst. This difference in behavior of CO 2 over cobalt and iron could be attributed to the absence of reverse water-gas shift activity on cobalt and hydrogenation of CO 2 to hydrocarbons-other than methane-will be derived through the formation of CO.
Correlation between Fischer-Tropsch catalytic activity and composition of catalysts
Chemistry Central Journal, 2011
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), COchemisorption, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM-EDX) and N 2-adsorption analysis. Fischer-Tropsch synthesis (FTS) was carried out in a fixed-bed microreactor at 543 K and 1 atm, with H 2 /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. H 2-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 C 5+ hydrocarbons (1.6%).