Promoted Iron Catalyst Research Articles

Copper, potassium promoted iron on metallosilicate and aluminum oxide supports synthesized via a non-hydrolytic sol-gel for Fischer-Tropsch

We developed a promoted iron based catalyst that converts 20% more CO to diesel than the unpromoted counterparts. The synthesis involves a non-hydrolytic sol-gel method (NHSG) and 0.04 g g−1 copper and 0.02 g g−1 potassium as promoters. The iron catalyst supports included cerium and zirconium metallosilicates and Catalox and Dispal commercial aluminum oxides from Sasol. At 325 ∘C and 20 bar, CO conversion over the Fe/Ce/SiO2-K,Cu, exceeded 85% while at the same conditions it was only 68% over the unpromoted catalyst. Fe/Zr/SiO2-K,Cu converted less CO than the cerium-silicate (75%) but the unpromoted zirconium-silicate only converted 43% of the CO. The conversion and selectivity of the Catalox was about the same as the cerium-silicate, while the Dispal performance was equivalent to the zirconium-silicate. This study also highlights the importance of support and promoters in FTS, demonstrates the potential of the NHSG method to synthesize promoted iron catalysts with various supports and lays the foundation for developing efficient and stable catalysts for converting syngas to hydrocarbons.

Catalytic Behavior and In Situ X‐Ray Diffraction of Promoted Iron Catalysts for Fischer‐Tropsch Synthesis

AbstractThe effects of structural promoters (ZnO, SiO2, and Al2O3) on the phase transformation during reduction and Fischer‐Tropsch synthesis (FTS) of a FeCuK catalyst were investigated by in situ X‐ray diffraction and the FTS catalytic performance was studied in a fixed‐bed reactor. The reduction follows the path of Fe2O3/K2Fe22O34 → Fe3O4 → α‐Fe. The addition of ZnO, SiO2, and Al2O3 delayed and prolonged the reduction. The iron carbides formed under reaction conditions were χ‐Fe5C2 and ε‐Fe2C. The presence of ZnO, SiO2, and Al2O3 favored the formation of χ‐Fe5C2. ε‐Fe2C is a more active phase. Besides, ε‐Fe2C seems to favor the formation of CO2 and C5+ and χ‐Fe5C2 benefits CH4 and C2–C4 products.

Modifying the Hydrogenation Activity of Zeolite Beta for Enhancing the Yield and Selectivity for Fuel-Range Alkanes from Carbon Dioxide.

In order to empower a circular carbon economy for addressing global CO2 emissions, the production of carbon-neutral fuels is especially desired, since addressing the global fuel demand via this route has the potential to significantly mitigate carbon emissions. In this study, we report a multifunctional catalyst combination consisting of a potassium promoted iron catalyst (Fe-K) and platinum containing zeolite beta (Pt-beta) which produces an almost entirely paraffinic mixture (up to C10 hydrocarbons) via CO2 hydrogenation in one step. Here, the Fe catalyst is responsible for modified Fischer-Tropsch synthesis from CO2 while Pt-beta is instrumental in tuning the product distribution almost entirely towards paraffins (both linear and branched) presumably via a combination of cracking and hydrogenation. The optimal temperature of operation was estimated to be 325 °C for the production of higher paraffins (C5 -C10 ) with a selectivity of ca. 28 % at a CO2 conversion of ca. 31 %.

Methane decomposition over strontium promoted iron catalyst: effect of different ratio of Al/Si support on hydrogen yield

The performance of a 5% Sr-promoted Fe catalyst on CH4 decomposition was investigated with the aid of catalysts to produce hydrogen gas and carbon. The catalysts consisted of 20% Fe and support mixtures of Al2O3 and SiO2 in various ratios (Al2O3/SiO2: 100/0.00, 90.0/10.0, 80.0/20.0, and 0.0/100.0). The catalysts were prepared via the impregnation method, calcination temperatures of 800 °C and 900 °C, and activation temperature at 800 °C. BET, XRD, H2-TPR, and TGA characterizations were employed to describe the physicochemical properties of the catalysts (SA-0, SA-10, SA-20, and SA-100). For the catalyst supported only with silica, no reaction was observed for all the considered temperatures. The Al/Si-20 catalyst calcined at 900 °C and reacted at 800 °C gave the optimal average hydrogen yield of about 80%. The Al/Si-20 sample promoted with 5% Sr provided a higher average H2 yield of around 84%. Moreover, the Sr-promoted catalyst improved stability by depressing the carbon deposition by 26%.

Development and application of wüstite-based ammonia synthesis catalysts

In the 1980s, Zhejiang University of Technology (ZJUT) started developing a new catalyst for ammonia synthesis which in final form comprises multi-promoters wüstite-based catalysts with Fe1-xO as precursor. This became the first new iron catalyst for ammonia synthesis commercialized since Fritz Haber’s promoted iron catalyst. The catalyst is commercialized in the existing or new low pressure process. In this paper, the basic theory, method, technology and practice of the wüstite-based catalyst in industrial production and application are reviewed. The wüstite-based catalysts are still iron-based, however, they are completely different from the magnetite-based catalyst in the preparation principle, chemical composition, crystal structure, and chemical-physical properties. Wüstite does not exist in nature, and is a thermodynamically meta-stable phase. Therefore, the Fe1-xO must be firstly synthesized by a chemical method and avoid occurrence reactions of oxidation and disproportionation to obtain a commercial wüstite-based catalyst with single phase and stability during the preparation of catalyst. We described the development of the catalyst, starting from the 1980s with studies to elucidate the inhibition mechanism of disproportionation reaction and the effects of temperature and promoters, and to ensure that a single wüstite phase is obtained during preparation. This is a prerequisite for ensuring high activity of the catalyst. Scale up of catalyst production and testing were described briefly, as are some process considerations. Secondly, we described the industrial application of the catalyst with studies to elucidate including the industrial bypass testing, the foundation research on the industrial application technology such as industrial reduction technology due to too fast reduction rate, development of industrial technology taking out the excess reaction heat, optimization of reaction conditions using wüstite-based catalyst, low-pressure ammonia process, and optimization of synthesis loop process and convertor for existing synthesis ammonia plant, etc. The wüstite-based catalysts exhibit about 70 % higher catalytic activity, and 65.9 % higher the TOF. It is the most advanced commercial iron catalyst with the highest activity and low production cost in the world, and it is competitive with ruthenium-based ammonia synthesis catalysts. In industrial application, compared to the classic magnetite-based catalyst for ammonia synthesis, the higher activity allows lower operating temperatures and loop pressures. Existing loops can utilize it by running at minimum possible loop pressure for extended period of time. This allows to increase ammonia plant performance, efficiency and economy without the need of any revamping. New plants could be designed for lower pressure operation and with a smaller synthesis converter. This all together leads to lower capital expend tureen lower energy costs. The activation of this catalyst is fast and easy, which saves time and cost. Wüstite-based catalyst is clearly a perfect low cost alternative to Ru/C catalyst.

Increased CO2 hydrogenation to liquid products using promoted iron catalysts

The effect of alkali promoter (K, Rb and Cs) on the performance of precipitated iron-based catalysts was investigated for carbon dioxide (CO2) hydrogenation. Characterization by temperature-programmed reduction with CO, Mössbauer spectroscopy, and transmission electron microscopy were used to study the effect of alkali promoter interactions on the carburization and phase transformation behavior of the catalysts. Under similar reaction conditions, cesium (Cs) and rubidium (Rb) promoted catalysts exhibited the highest initial CO2 conversions to higher hydrocarbons. CO2 conversions then decreased to reach steady state conversions around 170 h on stream. At steady state conversion, all three catalysts exhibited similar CO2 conversions and selectivities. For comparison, a lower loaded Cs (1.5 Cs) promoted iron-based catalyst was prepared. It exhibited slightly lower initial conversion than the higher loaded Cs catalyst, but remained very stable. Among all the catalysts at steady state conversion, the 1.5 Cs promoted catalyst exhibited the highest stability. Results indicate a synergistic effect brought on by these promoters that, if balanced, could potentially yield superior CO2 hydrogenation catalysts.

Performance of Promoted Iron/CNT Catalyst for Fischer–Tropsch Synthesis: Influence of Pellet Shapes and Binder Loading

Instead of powder, catalyst pellets are preferred in a fixed-bed reactor for Fischer–Tropsch synthesis (FTS). In this research, promoted iron catalysts supported on carbon nanotubes (CNT) were pelletized in two different shapes (spherical and cylindrical) using different bentonite loadings (10–20 wt %). The pellets were tested for mechanical strength using single pellet and bulk crushing test methods (ASTM D 4179, 6175, and 7084). The spherical pellets were found to sustain higher crushing strength as compared to cylindrical pellets. However, both spherical and cylindrical Fe/CNT pellets with 20 wt % bentonite loading were found to be mechanically stronger than commercial alumina spherical pellets, suggesting their suitability in fixed bed reactors. The pellets were characterized to determine the change in active metal dispersion and ease in reducibility based on their shape and binder content using CO chemisorption, XRD, and H2-TPR. The cylindrical shaped pelleted catalysts were found to be easy to reduc...

The catalytic performance of different promoted iron catalysts on combined supports Al2O3 for carbon dioxide hydrogenation

Global warming, fossil fuel depletion and fuel price increases have motivated scientists to search for methods for the storage and reduction of the amount of greenhouse gases, especially CO2. The hydrogenation process has been introduced as an emerging method of CO2 capture and convertion into value-added products. In this study, new types of catalysts are introduced for CO2 hydrogenation and are compared based on catalytic activity and product selectivity. The physical properties of the samples are specified using BET. Iron catalysts supported on γ-Al2O3 with different metal promoters (X = Ni, K, Mn, Cu) are prepared through the impregnation method. Moreover, Fe–Ni catalysts supported on HZSM5-Al2O3 and Ce–Al2O3 are synthesized. Samples are reduced by pure H2 and involved in hydrogenation reaction in a fixed bed reactor (H2/CO2 = 3, total pressure = 10 MPa, temperature = 523 K, GHSV = 2000, 1250 nml/min). All catalysts provide high conversion in hydrogenation reactions and the results illustrate that the selectivity of light hydrocarbons is higher than that of methane and CO. It is found that Ni has a promoting effect on the conversion fluctuations throughout the reaction with 66.13% conversion. Using combined supported catalysts leads to enhancing catalytic performance. When Fe–Ni/γ–Al2O3—HZSM5 is utilized, CO2 conversion is 81.66% and the stability of the Fe–Ni catalyst supported on Al2O3 and Ce–Al2O3 furthey improves.

1-5.石炭液化反応における鉄触媒の活性(Session(1)石炭転換反応における触媒の役割)

1-5.石炭液化反応における鉄触媒の活性(Session(1)石炭転換反応における触媒の役割)

Ammonia Synthesis at Reduced Pressure via Reactive Separation

Ammonia is normally made at high temperature and pressure using a promoted iron catalyst. High temperatures are needed to get fast kinetics; the high pressure is used to ensure high conversion. Alternatively, ammonia can be made at high temperature but lower pressure if the product ammonia is rapidly separated. Here, we have systematically studied the effect of temperature and pressure on the rates of reaction. We then have qualitatively investigated the absorptive separation of ammonia using calcium chloride in a reaction–separation process. Rapid separation reduces the constraint of reversible reaction and enables us to obtain appropriate reaction rates at relatively lower pressure. The effect of different operating conditions—reaction temperature, pressure, absorption temperature, and gas transport—on production rates is carefully measured, and this elucidates the potential and the limits of this type of low-pressure ammonia synthesis.

Fischer–Tropsch Mechanism: 13C18O Tracer Studies on a Ceria–Silica Supported Cobalt Catalyst and a Doubly Promoted Iron Catalyst

Tracer studies were performed on cobalt and iron Fischer–Tropsch catalysts using a synthesis gas containing a 20:80 mixture of 13C18O and 12C16O. The objective of the work was to investigate the antecedents of the C–O bonds in alcohols and CO2 formed during Fischer–Tropsch (FT) synthesis. It was found that chain growth proceeded by a CO insertion mechanism over both cobalt and iron catalysts. Over the cobalt catalyst, the dominant pathway for methanol synthesis involved a partial hydrogenation of CO as well as CO2 by a reaction pathway separate from the Fischer–Tropsch pathway. Over the iron catalyst, the majority of the methanol was formed by partial hydrogenation of only CO through the FT reaction pathway. Iron is active for water gas shift conversion, which produced CO2. Oxygen exchange reactions of CO2 were likely over both catalysts and complicated the interpretation of the results.

Steam gasification of safflower seed cake and catalytic tar decomposition over ceria modified iron oxide catalysts

Catalytic steam gasification of safflower seed cake was carried out using a double-bed microreactor in a two-stage process in the presence of ceria oxide (CeO2) modified iron oxide (Fe2O3) catalysts with different CeO2–Fe2O3 ratios. The effects of both catalyst and the temperature of catalytic bed on the tar decomposition and the overall gaseous product yield were investigated comparatively. It was found that ceria modified iron oxide catalysts had higher reactivity than that of the individual Fe2O3 and CeO2 for the catalytic tar decomposition in safflower seed cake steam gasification. The CeO2–Fe2O3 catalyst with 50wt.% of Fe2O3 exhibited the excellent performance for tar conversion at 700°C. A comparison of tar decomposition from thermal run and catalytic run showed that in thermal run tar decomposition was progressed via steam reforming only. However, in the presence of catalyst, tar decomposition occurred via both steam reforming and water gas shift reaction. As a conclusion, ceria promoted iron catalysts were found to be active for both hydrogen production and tar decomposition in steam gasification of lignocellulosic biomass.

Fischer–Tropsch Synthesis: Branched Paraffin Distribution for Potassium Promoted Iron Catalysts

Iron Fischer–Tropsch catalysts with varying amounts of K (0, 2, 4, 6, 10 wt%) were utilized. Except possibly for the 10 wt% catalyst, the amount of the iso-alkanes produced was essentially constant for carbon numbers from 4 to 23. Iso-alkanes accounted for about 13–15 % of the hydrocarbon products that were produced. The 2- and 3-methyl isomers were present at about two times the amount of the other methyl isomers for each carbon number. Mechanisms to account for the branching were considered but a satisfactory one could not be found.

The Genesis and Development of the Commercial BP Doubly Promoted Catalyst for Ammonia Synthesis

In the 1970s BP started developing a new catalyst for ammonia synthesis which in final form comprises ruthenium, two promoters and a graphitised carbon support. This became the first new catalyst for ammonia synthesis to be commercialised since Fritz Haber’s promoted iron catalyst. The catalyst is commercialised in the KBR Advanced Ammonia Process (KAAP). We describe the development of the catalyst, starting in the 1960s with studies to elucidate the mechanism of selective hydrogenation catalysts using nickel single crystals and LEED. These identified a phenomenon dubbed surface reorientation, in which an adsorbate such as sulphur causes the structure of the surface monolayer of a metal to change e.g. from fcc [111] to [100]. These ideas led to discovery of an active platinum/alkali metal/carbon catalyst for the dehydrocyclisation of hexane. That catalyst was not commercial, but it led in turn to the identification of highly active ruthenium/alkali metal/carbon catalysts for ammonia synthesis. The best new catalyst is about 20 times more active than a commercial Haber catalyst. The special carbon support is mesoporous and graphitic. Scale up of catalyst production and testing are described briefly, as are some process considerations.

CO2 reactivity on Fe–Zn–Cu–K Fischer–Tropsch synthesis catalysts with different K-loadings

In the presence of low cost H2, the hydrogenation of pure CO2 streams (e.g., from carbon capture processes) or CO/CO2 mixtures (e.g., from biomass of coal gasification) to fuels is a potential solution to convert the primary greenhouse gas into a valuable building block for the synthesis of high-added value products. Iron based Fischer–Tropsch catalysts, known for their reverse water gas shift activity, are good candidates to run such process. However, their reactivity depends on the catalyst formulation which may vary significantly in the presence of supports or promoters. Also, the H2/COx inlet ratio may strongly influence the catalyst activity and selectivity. With the purpose of gaining more insights into the reactivity of carbon dioxide, the catalytic performances of K-promoted 100Fe/10Zn/1Cu samples have been comparatively studied in CO, CO2, and CO/CO2 hydrogenation processes with low H2/COx ratios varying from 0.5 to 1. We have found that traditional iron-based catalysts for the Fischer–Tropsch synthesis can be successfully used to obtain high added-value products from CO2 even in the presence of H2 deficient feed streams. In the case of pure CO2 hydrogenation, the most promising results are obtained with strong potassium promoted iron catalysts which grant interesting selectivities toward middle distillates by favoring CO2 adsorption. In the presence of strongly adsorbed CO, CO2 is instead hardly converted independently on the K-loading. The presence of CO2 does not affect the product distribution either. Nevertheless, CO2 has a key-role in preventing the CO shift to CO2, thus improving the overall economy of the conversion process and avoiding a net CO2 production. Interestingly, upon increasing the K-loading, the CO conversion rate is decreased, both in the presence and in the absence of CO2, possibly as a result of the very strong CO adsorption on the catalytic surface. Such result is however complicated by the presence of initial deactivation phenomena, whose rates may be also related to the K-loading of the catalyst. Accordingly, the best catalyst formulation appears to be significantly different depending on the presence of CO in the feed.

Thermodynamic analysis of nanoparticle size effect on kinetics in Fischer–Tropsch synthesis by lanthanum promoted iron catalyst

The kinetic parameters of the Fischer–Tropsch synthesis (FTS) on iron catalyst are analyzed by size-dependent thermodynamic method. A Langmuir–Hinshelwood kinetic equation is considered for evaluation of catalytic activity of lanthanum promoted iron catalyst. A series of unsupported iron catalysts with different particle sizes were prepared via microemulsion method. The experimental results showed that catalyst activity pass from a maximum value by increasing the iron particle size. Also, data presented that iron particle size has considerable effects on adsorption parameters and FTS rates. The ratio of surface tension (σ) to nanoparticle radius (r) is important in FTS reaction on iron catalyst. Finally, the results showed that by increasing of iron particle size from 18 to 45 nm the activation energies of catalysts and heats of adsorption of catalysts as two main parameters of FTS reaction increased from 89 to 114 kJ/mol and from 51 to 71 kJ/mol, respectively.

The application of synchrotron methods in characterizing iron and cobalt Fischer–Tropsch synthesis catalysts

This article reviews the use of synchrotron radiation techniques to confront issues associated with cobalt and iron catalysts. The main areas that are examined include: (1) the application of TPR-XANES and TPR-EXAFS to gain insight into the hydrogen reduction of cobalt catalysts and the carburization of iron catalysts; (2) the impact of promoters on these reduction/carburization rates; (3) the local atomic structure of promoters and its influence on catalyst selectivity; (4) exploring the deactivation of cobalt catalysts; (5) the influence of crystallite size in stabilizing cobalts catalyst against water effects; and (6) temperature effects in alkali promoted iron catalysts in retaining the iron carbide phase against reoxidation by water.

Modeling of Fischer-Tropsch Product Distribution over Fe-based Catalyst

The kinetic models of Fischer-Tropsch synthesis (FTS) product distribution can be classified into two major groups: hydrocarbon selectivity models and detailed Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic models. In this study the two approaches to FTS product distribution modeling are presented and compared using the experimental data obtained in a stirred tank slurry reactor with promoted iron catalyst over a wide range of process conditions. Positive deviations from the classical Anderson-Schulz-Flory distribution and an exponential decrease in olefin-to-paraffin ratio with carbon number are predicted by the inclusion of solubility-enhanced 1-olefin readsorption and/or chain length dependent 1-olefin desorption concepts. In general the agreement between the model predictions and experimental data was very good, and modeling approaches are discussed in terms of fit quality, physical meaningfulness and practical utility.

Fischer–Tropsch Synthesis: Deuterium Kinetic Isotope Study for Hydrogenation of Carbon Oxides Over Cobalt and Iron Catalysts

The hydrogenation of CO2 using Pt promoted Co/γ-Al2O3 and doubly (Cu, K) promoted iron catalysts exhibits an inverse isotope effect (r H/r D < 1). The observed inverse isotope effect for hydrogenation of CO2 shows that hydrogen addition to CO2 should be involved in the kinetically relevant step. The systematic increase of inverse isotope effect with carbon number of products obtained during H2–D2–H2 switching experiments suggests the possible existence of a common intermediate (CH x O) for hydrogenation of CO2 over both cobalt and iron FT catalysts. The magnitude of the inverse isotope effect is lower for CO2 compared to CO hydrogenation under similar reaction conditions. The deuterium isotope effect does not provide a definite conclusion regarding the mechanism which CO2 hydrogenation follows (alkyl, enol, or alkylidine mechanisms).

Fischer–Tropsch synthesis: Attempt to tune FTS and WGS by alkali promoting of iron catalysts

The effect of water on the performance of alkali-promoted, precipitated Fe catalysts was investigated during Fischer–Tropsch (FT) synthesis in a continuously stirred tank reactor. In these studies, the added water (5–25 mol%) replaced an equivalent amount of inert gas so that all other reaction conditions remained the same before, during and after water addition. The externally added water had a positive effect on the CO conversion for all the alkali-promoted, precipitated iron catalysts. The impact of the added water is to increase the rate of the water-gas shift (WGS) reaction with up to 10–15 mol% added water, and then leveling off for further increases in the amount of water added to the feed gas. Increasing the water amount in the feed gas caused the fraction of CO converted into hydrocarbons to decrease and both the WGS activity and the oxygenate selectivity to increase. Common for all the alkali promoted iron catalysts was a decrease in C 5+ selectivity and an increase in the methane selectivity with increasing amounts of water up to 10–15 mol%; with further increases of water, the C 5+ selectivity increases and methane selectivity decreases. Methane selectivity is directly correlated to the CO conversion and H 2/CO ratio inside the reactor.