Conversion Of Synthesis Gas Research Articles

Effects of preparation and operation conditions on precipitated iron nickel catalysts for Fischer-Tropsch synthesis

Iron nickel oxide catalysts were prepared using co-precipitation procedure and studied for the conversion of synthesis gas to light olefins. In particular, the effects of a range of preparation variables such as [Fe]/[Ni] molar ratios of the precipitation solution, precipitate aging times, calcination conditions, different supports and loading of optimum support on the structure of catalysts and their catalytic performance for the tested reaction were investigated. It was found that the catalyst containing 40%Fe/60%Ni/40wt%Al 2O 3, which was aged for 180 min and calcined at 600 °C for 6 h was the optimum modified catalyst. The catalytic performance of optimal catalyst has been studied in different operation conditions such as reaction temperatures, H 2/CO molar feed ratios and reaction total pressure. Characterization of both precursors and calcined catalysts was carried out by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area measurements, thermal analysis methods such as thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC).

Ethanol synthesis from syngas over Rh-based/SiO 2 catalysts: A combined experimental and theoretical modeling study

Catalytic conversion of biomass-derived synthesis gas to ethanol and other C 2 + oxygenates has received considerable attention recently due to the strong demands for alternative, renewable energy sources. Combining experimental measurements with first-principles-based kinetic modeling, we investigated the reaction kinetics of ethanol synthesis from CO hydrogenation over SiO 2 -supported Rh/Mn alloy catalysts. We find that an Mn promoter can exist in a binary alloy with Rh and play a critical role in lowering the CO insertion reaction (CO + CH x ( x = 1–3)) barriers thus improving the selectivity toward ethanol and other C 2 + oxygenates, although the barrier toward methane formation is unaffected. The postulation of supported Rh/Mn alloy nanoparticle being the active phase is supported by our experimental characterization using X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray diffraction of practically used Rh/Mn/SiO 2 catalysts. First-principles density functional theory (DFT) calculations further confirmed that the binary Rh/Mn alloy is thermodynamically more stable than the mixed metal/metal oxides under the reducing reaction condition. The reaction kinetics of CO hydrogenation to ethanol on the three-dimensional Rh/Mn nanoparticle under experimental operating conditions was studied using kinetic Monte Carlo (KMC) simulations. The simulated reaction kinetics is qualitatively consistent with experimental observations. Finally, the effects of various promoters (M = Ir, Ga, V, Ti, Sc, Ca, and Li) on the CO insertion reaction over Rh/M alloy nanoparticles were investigated using DFT calculations. We found alloying the promoters with the electronegativity difference, Δ χ, between the promoter (M) and Rh being 0.7 is the most effective in lowering the barriers of CO insertion reaction, which leads to higher selectivity to ethanol. This conclusion is in excellent accord with the reported catalytic performance of CO hydrogenation over Rh-based catalysts with different promoters. We believe that the electronegativity difference criterion is very useful in improving the catalytic performance using transition metal-based catalysts for ethanol synthesis from CO hydrogenation.

Effect of forming on selectivity and attrition of co-precipitated Co–Mn Fischer–Tropsch catalysts

Cobalt–manganese catalyst is widely studied in Fischer–Tropsch synthesis to obtain light olefins from synthesis gas. However, selectivity and mechanical strength of the catalyst differ depending on its preparation method and type of reactor. The main objective of this paper is to develop a better understanding of manufacturing parameters affecting attrition strength and selectivity of the catalyst. The cobalt–manganese oxide nano-catalysts were prepared using co-precipitation method. The fine powders were then formed using tabletting–crushing (pelletizing) process to obtain the catalyst pellets. The original unformed and formed catalysts were explored for the conversion of synthesis gas to the light olefins in a standard laboratory fixed bed reactor considering selectivity to ethylene and propylene. The processing variables investigated were included of type and concentration of binder and compression pressure in pelletizing process. Furthermore, the attrition assessment of catalyst was carried out using a rotary bottle shake system. The results presented in this work revealed that forming the catalyst under 75 bar compression pressure and 4 wt.% Syton binder led to the maximum selectivity. In the attrition evaluation, it was found that the extent of attrition was the least at the same forming conditions (75 bar, 4 wt.% Syton).

A study of K-promoted MoP–SiO 2 catalysts for synthesis gas conversion

The conversion of synthesis gas to oxygenated hydrocarbons over a series of K-promoted MoP–SiO 2 catalysts, is reported. Catalysts with 5, 10, and 15 wt% MoP on SiO 2 and promoted with 1 and 5 wt% K, were prepared, characterized and tested at 548 K, 8.27 MPa and a H 2:CO = 1. An increase in CO conversion was observed with increased MoP and K loading and the highest oxygenate space time yield of 147.2 mg g cat −1 h −1 was obtained over the 5 wt% K–15 wt% MoP–SiO 2 catalyst. CH 4 was produced with high selectivity (29–40 C atom%) over the un-promoted MoP catalysts, but with the addition of K, the CH 4 selectivity was suppressed and the C 2+ oxygenated product selectivity increased as the surface K/Mo atom ratio increased, up to a maximum at a K/Mo ratio of 3.2. The highest selectivity towards C 2+ oxygenates (76.6 C atom%) and lowest selectivity towards CH 4 (9.7 C atom%) occurred on the 5 wt% K–10 wt% MoP–SiO 2 catalyst. The major oxygenates in the product were acetaldehyde, acetone and ethanol. In all cases, catalyst selectivity to methanol was low (<5 C atom%). The product distribution obtained over the K–MoP–SiO 2 catalysts was distinct from that reported on other Mo-based catalysts.

A DFT study of the effect of K and SiO2 on syngas conversion to methane and methanol over an Mo6P3 cluster

Synthesis gas (CO+H2) conversion to CH4 and CH3OH over an Mo6P3 cluster, an Mo6P3–Si3O9 and a K–Mo6P3–Si3O9 cluster has been studied using density functional theory (DFT). The study focused on the reaction between the intermediate species CH2OHad+Had, comparing methanol formation to C–O bond scission that yields CH2.ad+H2Oad species. The activation energies of both the reactions decreased on the Mo6P3–Si3O9 and the K–Mo6P3–Si3O9 clusters compared to the Mo6P3 cluster. However, on the K–Mo6P3–Si3O9 cluster, the activation energy for methanol formation (12.1 kcal/mol) was higher than the C–O bond-breaking activation energy (9.9 kcal/mol). Although the DFT study predicted preferential formation of CH4 versus CH3OH on all the Mo6P3 clusters, the study also predicted an increased formation of CH3OH with the addition of K and experimental measurements are in agreement with this prediction.

The effect of H2S on the selectivity of light alkenes in the FE-Mn-catalyzed Fischer-Tropsch synthesis

Iron-manganese oxides are prepared using a co-precipitation procedure and studied for the conversion of synthesis gas to light olefins. In particular, the effect of a range of preparation variables is investigated in details. In this investigation, sulfur absorption and effect of sulfur poisoning on Fe-Mn catalysts have been studied. In the Fischer-Tropsch synthesis process, the poisoning of the catalyst is one of the important parameters causing a decrease in the catalyst activity, declaring the sulfur compounds as virulent poisons in this process. In the present investigation, poisoning of Fe-Mn catalysts were performed in a gas circulation system and H2S was injected into a circulation loop. The prepared catalysts were exposed to a mixture of H2S and N2 at about 450°C in the stainless-steel micro reactor via co-precipitation method. H2S was produced by addition of H2SO4 to Na2S × H2O and this gas was mixed with an inert carrier gas (N2). Comparing the activity and selectivity of fresh and poisoned catalysts, indicates that the selectivity and CO conversion are affected by high-level sulfur adsorbed on the catalysts. The results show that the CO conversion and selectivity with respect to methane production and coke formation were decreased, but the selectivity of light alkenes such as propylene was increased over poisoned catalysts. Characterization of both precursors and calcined catalysts by powder X-ray diffraction, BET specific surface area and thermal analysis methods such as TGA and DSC showed that the poisoning of Fe-Mn catalysts influenced the catalyst structure.

Direct conversion of synthesis gas to light olefins using dual bed reactor

Fe–Cu–Al based FT catalyst and ZSM-5 cracking catalysts are employed in a consecutive dual bed reactor system for the production of C2–C4 olefins directly from synthesis gas. Effect of properties of FT and cracking catalysts on the CO conversion and product selectivity has been studied. The carburization and hydrogenation properties of catalysts related to chain propagation and termination reactions of FT catalyst are balanced by optimizing the K loading on Cu promoted Fe–Al FT catalyst. Alkalization with K resulted in the formation of Fe2O3 crystalline phase in FT catalyst, identified by XRD and this phenomenon has coincided with the suppression of chain termination reactions to yield enhanced C5+ hydrocarbons with minimum methane in synthesis gas conversion. Interestingly the olefinicity of light hydrocarbons is increased significantly after the K loading. The conceptualization of achieving higher C5+ olefinic products in FT followed by selective cracking of the C5+ into C2–C4 olefins has been realized by optimization of the properties of FT as well as ZSM-5 catalysts. The studies report an enthusiastic result that claims about 52% selectivity to C2–C4 hydrocarbon rich in olefins (77% selectivity).

Kinetic modeling for the conversion of synthesis gas to dimethyl ether on a mixed Cu-ZnO-Al2O3 catalyst with γ-Al2O3

A model is proposed for the kinetics of the direct conversion of synthesis gas to dimethyl ether (DME) on a bifunctional catalyst in a flow reactor. Calculations for the yield of methanol and DME were carried out using literature data for the kinetics of methanol synthesis and methanol dehydration.

Direct versus Hydrogen-Assisted CO Dissociation

The mechanism of CO dissociation is a fundamental issue in the technologically important Fischer-Tropsch (F-T) process that converts synthesis gas into liquid hydrocarbons. In the present study, we propose that on a corrugated Ru surface consisting of active sixfold (i.e., fourfold + twofold) sites, direct CO dissociation has a substantially lower barrier than the hydrogen-assisted paths (i.e., via HCO or COH intermediates). This proves that the F-T process on corrugated Ru surfaces and nanoparticles with active sixfold sites initiates through direct CO dissociation instead of hydrogenated intermediates.

Cover Picture: Nanoscale Chemical Imaging of the Reduction Behavior of a Single Catalyst Particle (Angew. Chem. Int. Ed. 20/2009)

AbstractIron‐based catalysts for the Fischer–Tropsch synthesis bring about the conversion of synthesis gas (CO/H2) derived from coal or biomass into liquid transportation fuels. In their Communication on page 3632 ff., B. M. Weckhuysen, F. M. F. de Groot, and co‐workers provide insights into the difference in behavior of the catalyst precursors during pretreatment in H2 on both the nanoscopic and the bulk scale. These findings enable further understanding of how the activated catalyst works.magnified image

Ruthenium Nanoparticles Supported on Carbon Nanotubes as Efficient Catalysts for Selective Conversion of Synthesis Gas to Diesel Fuel

AbstractDiesel erwünscht? Das Titelsystem ist ein hochselektiver Fischer‐Tropsch‐Katalysator für die Erzeugung von C10‐ bis C20‐Kohlenwasserstoffen (Dieseltreibstoff). Die Selektivität für diese Kettenlängen hängt stark von der Größe der Ru‐Nanopartikel ab. Nanopartikel mit Größen um 7 nm zeigen die höchste Selektivität (ca. 65 %) bei außerdem hohen CO‐Umsatzfrequenzen.magnified image

Ruthenium Nanoparticles Supported on Carbon Nanotubes as Efficient Catalysts for Selective Conversion of Synthesis Gas to Diesel Fuel

Diesel do nicely: The title system is a highly selective Fischer-Tropsch catalyst for the production of C(10)-C(20) hydrocarbons (diesel fuel). The C(10)-C(20) selectivity strongly depends on the mean size of the Ru nanoparticles. Nanoparticles with a mean size around 7 nm exhibit the highest C(10)-C(20) selectivity (ca. 65%) and a relatively higher turnover frequency for CO conversion.

The Application of Zeolites and Periodic Mesoporous Silicas in the Catalytic Conversion of Synthesis Gas

In the recent years there has been a rising interest in the conversion of remote and abundant natural gas as well as renewable biomass sources into high quality fuels and valuable raw chemicals via synthesis gas (syngas, CO + H2) as a versatile intermediate. The metal catalysed CO hydrogenation can be selectively directed towards hydrocarbons as precursors of ultra clean liquid fuels (Fischer-Tropsch synthesis) or to added-value products such as light olefins and oxygenates (alcohols, carboxylic acids, ethers, etc.). By taking advantage of their unique and tunable structural and chemical properties, inorganic molecular sieves such as zeolites and periodic mesoporous silicas have been extensively explored as effective components of heterogeneous catalysts for the selective conversion of syngas. Thus, ordered mesoporous silicas (MCM-41, MCM-48, SBA-15) have shown interesting properties as catalytic supports for Co and Fe based Fischer-Tropsch catalysts. Besides, zeolite-entrapped mono and bimetallic clusters have been reported to selectively direct the synthesis towards oxygenates. In this work, the use of the original structural properties of these materials to tailor the dispersion, geometrical location and chemical state of metallic sites leading to heterogeneous catalysts with enhanced activity and selectivity in syngas catalytic routes is reviewed. The introduced peculiarities, benefits and drawbacks of these structured solids in comparison to conventional amorphous supports are also discussed.

Fischer‐Tropsch Synthesis over Iron Manganese Catalysts: Effect of Preparation and Operating Conditions on Catalyst Performance

Iron manganese oxides are prepared using a coprecipitation procedure and studied for the conversion of synthesis gas to light olefins and hydrocarbons. In particular, the effect of a range of preparation variables such as [Fe]/[Mn] molar ratios of the precipitation solution, pH of precipitation, temperature of precipitation, and precipitate aging times was investigated in detail. The results are interpreted in terms of the structure of the active catalyst and it has been generally concluded that the calcined catalyst (at 650 ∘C for 6 hours) containing 50%Fe/50%Mn‐on molar basis which is the most active catalyst for the conversion of synthesis gas to light olefins. The effects of different promoters and supports with loading of optimum support on the catalytic performance of catalysts are also studied. It was found that the catalyst containing 50%Fe/50%Mn/5 wt.%Al2O3 is an optimum‐modified catalyst. The catalytic performance of optimal catalyst has been studied in operation conditions such as a range of reaction temperatures, H2/CO molar feed ratios and a range of total pressures. Characterization of both precursors and calcined catalysts is carried out by powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area and thermal analysis methods such as TGA and DSC.

Alter NRG to build Canada's first CTL plant

The Fischer–Tropsch synthesis represents a time-tested and fully proven technology for the conversion of synthesis gas (CO + H2) into paraffins, olefins, and oxygenated hydrocarbons. Depending on the origin of the syngas, one speaks of gas-to-liquids, coal-to-liquids, biomass-to-liquids, or ‘anything’-to-liquids. Industrial Fischer–Tropsch plants run on iron or cobalt catalysts, in fixed-bed-, fluidized-bed-, or slurry bubble-column-type reactors. The Fischer–Tropsch synthesis has inspired a wealth of academic and industrial research, and questions as to the mechanism of the process, how to control the selectivity of the polymerization process, the surface structure of the active catalysts, and the reasons why the catalysts deactivate continue to be subjects of intense discussion at conferences and in the literature. This chapter presents an overview of the Fischer–Tropsch synthesis, its historical development, the different modes of operation, the reactor technology, the synthesis and characteristics of the catalysts, and the mechanism of the reactions.

Synthesis gas conversion over MoP catalysts

Abstract Synthesis gas conversion at 548 K, 8.3 MPa and a H 2 /CO = 1 over a 10 wt% MoP on SiO 2 catalyst yielded mostly hydrocarbons with 35% selectivity to methane. K addition to the MoP–SiO 2 shifted selectivity to oxygenates. With 5 wt% K–MoP–SiO 2 the major products were acetaldehyde (14.3%), acetone (13.5%) and ethanol (17.2%), with −1 h −1 and the methane selectivity was 9%. The low methanol and methane selectivities reported herein are unique among the Mo-based synthesis gas conversion catalysts.

A study of synthesis gas conversion to methane and methanol over a Mo6P3 cluster using density functional theory

Synthesis gas (CO+H2) conversion to CH4 and CH3OH over a MoP catalyst has been examined using density functional theory and a Mo6P3 cluster model of the MoP surface. A model of synthesis gas conversion was developed by calculating adsorption energies of all possible arrangements of stable surface intermediates on Mo6P3. For CH4 formation, the potential energy surface (PES) followed the route (Had addition at each step is assumed but not shown) COad → CHOad → CH2Oad → CH2OHad → CH2.ad+H2Oad → CH3.ad+H2Oad → CH4+H2O and CH3OH followed COad → CHOad → CH2Oad → CH2OHad → CH3OHad. The activation energy for the formation of CH3OH from hydroxymethyl (100.9 kcal/mol) is higher than for the formation of methylene and water (40.3 kcal/mol), suggesting that CH4 rather than CH3OH will be produced from synthesis gas over MoP catalysts.

Fischer–Tropsch synthesis: A review of water effects on the performances of unsupported and supported Co catalysts

Abstract Fischer–Tropsch synthesis (FTS) process aims at converting synthesis gas to liquid fuels. Due to high activity and long catalyst life, cobalt-based catalyst is currently the catalyst of choice for gas to liquid (GTL) technology. Water is most undesirable byproduct of FTS process. Due to low water–gas-shift (WGS) activity of cobalt-based catalyst, the water concentration rises with time-on-stream (TOS) in FTS. This paper reviews the effects of water on the performances of various cobalt catalysts for FTS. The effects of water on FTS is quite complex and depends on the support and its nature, Co metal loading, its promotion with noble metals, and preparation procedure. Added water up to certain concentrations has positive effects (in terms of higher CO conversion, C 5+ selectivity, olefin selectivity and lower methane and CO 2 selectivity) on unsupported cobalt oxide catalysts. If the effects of support are taken into account, water has positive effect for silica-supported catalysts. The effects are negative for alumina where as for titania support, water has little positive effect. However in general, oxidation of cobalt active site depending on the cluster size and water partial pressure, the removal of transport restrictions via the formation of water-rich intra-pellet liquids, and kinetic effects have been considered as the main responsible factors. The effects are strongly influenced by the cobalt cluster size as well as on pore size of the support. Addition of noble metals at low cobalt loading increases the dispersion of cobalt on the support and hence improves its activity. Higher cobalt dispersion enhances the negative impact of water especially at higher water partial pressures under FTS conditions.

Toward Three-Dimensional Nanoengineering of Heterogeneous Catalysts

Cobalt-based Fischer-Tropsch systems are widely used to convert synthesis gas to clean hydrocarbon fuel. However, surprisingly little is known about the morphology of the catalysts on the nanoscale. Here we show that scanning transmission electron tomography reveals their true 3-D morphology and provides direct evidence that the support controls the final morphology of the catalyst. Such direct local three-dimensional measurements provide unprecedented insight into catalysis, and can henceforth transform our understanding of these complex materials.

SEM and BET Methods for Investigating the Structure and Morphology of Co - Ce Catalysts for Production of Light Olefins

Co–Ce catalysts prepared by the coprecipitation method were tested for production of light olefins. The effect of different preparation conditions including the [Co]/[Ce] molar ratio, aging time, calcination conditions, different supports, and loading of optimum support on the structure and catalytic performance of different catalysts were investigated. It was found that catalyst containing 80% Co/20% Ce/15% SiO2, which was aged for 2 h and calcined at 600°C for 6 h, is the optimum modified catalyst for the conversion of synthesis gas to light olefins. Characterization of both precursors and calcined catalysts (before and after the test) was carried out using scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) specific surface area measurements. The morphology of the catalysts was investigated by SEM and the surface areas of these catalysts were studied by BET. It was shown that all of the different preparation variables influenced the morphology and also the specific surface area of the catalyst precursors and calcined catalysts.