Chemisorption of C3 hydrocarbons on cobalt silica supported Fischer–Tropsch catalysts

Chemisorption of propene and propane was studied in a pulse reactor over a series of cobalt silica-supported Fischer–Tropsch catalysts. It was shown that interaction of propene with cobalt metal particles resulted in its rapid autohydrogenation. The reaction consists in a part of the propene being dehydrogenated to surface carbon and CH_x chemisorbed species; hydrogen atoms released in the course of propene dehydrogenation are then involved in hydrogenation of remaining propene molecules to propane at 323–423 K or in propene hydrogenolysis to methane and ethane at temperatures higher than 423 K. The catalyst characterization suggests that propene chemisorption over cobalt catalysts is primarily a function of the density of cobalt surface metal sites. A correlation between propene chemisorption and Fischer–Tropsch reaction rate was observed over a series of cobalt silica-supported catalysts. No propane chemisorption was observed at 323–373 K over cobalt silica-supported catalysts. Propane autohydrogenolysis was found to proceed at higher temperatures, with methane being the major product of this reaction over cobalt catalysts. Hydrogen for propane autohydrogenolysis is probably provided by adsorbed CH_x species formed via propane dehydrogenation. Propene and propane chemisorption is dramatically reduced upon the catalyst exposure to synthesis gas (H₂/CO = 2) at 323–473 K. Our results suggest that cobalt metal particles are probably completely covered by carbon monoxide molecules under the conditions similar to Fischer–Tropsch synthesis and thus, most of cobalt surface sites are not available for propene and propane chemisorption.     

Preparation of hierarchically meso-macroporous hematite Fe2O3 using PMMA as imprint template and its reaction performance for Fischer–Tropsch synthesis

The paper described a facile approach to prepare hierarchically meso-macroporous hematite Fe₂O₃ using PMMA as imprint template and its catalytic reaction in Fischer–Tropsch synthesis (FTS). The mixed solution of iron nitrate with ethylene glycol (EG) and methanol was infiltrated into the void of the colloidal crystal of a poly(methyl methacrylate) (PMMA) sphere with size in several microns. Heating initiated nitrate oxidation of the EG to produce metal glyoxylate salt. Further heating converted the glyoxylate salt to metal oxide and the skeleton of PMMA was reserved, which produced the hierarchically mesoporous and macroporous hematite Fe₂O₃. The fabricated iron oxide was applied to catalyze the FTS, showing high reaction activity and stability in comparison with the conventional Fe FTS catalyst.     

Ruthenium promotion of Co/SBA-15 catalysts with high cobalt loading for Fischer–Tropsch synthesis

30 wt.%Co/SBA-15 catalysts with different ruthenium contents (0.05–0.5 wt.%) were prepared by incipient wetness impregnation and characterized by diffuse reflectance infrared fourier transform spectroscopy, N₂ adsorption-desorption, X-ray diffractometry, temperature-programmed reduction and H₂ desorption, oxygen titration as well as X-ray photoelectron spectroscopy. The addition of a small amount of Ru promoter to Co/SBA-15 shifted the reduction temperature of both steps (Co₃O₄ → CoO and CoO → Co⁰) to lower temperatures and suppressed the formation of Co²⁺ species. After reduction, ruthenium atoms were encapsulated partially with cobalt cluster. There was no strong electronic interaction between metal cobalt and ruthenium, however, hydrogen spillover from ruthenium to cobalt oxide clusters occurred. With increasing ruthenium content, catalyst reducibility increased and the surface was enriched in cobalt atoms. Moreover, the peak intensities of both the linear and bridge types CO adsorption increased with the increase of ruthenium content, enhancing the catalytic activity on Fischer–Tropsch synthesis.     

Synthesis of Ag promoted porous Fe3O4 microspheres with tunable pore size as catalysts for Fischer–Tropsch production of lower olefins

Ag promoted porous Fe₃O₄ microspheres with tunable pore size were synthesized via one-pot solvothermal method and employed as catalysts for Fischer–Tropsch synthesis. The introduction of Ag played an important role in regulating the pore size of catalysts and the dispersion of Fe. Comparable to unmodified catalyst in this system, Ag promoted Fe-based catalysts displayed excellent selectivity to lower olefins, particularly for Fe–0.9Ag with smaller pore size of 1.33 nm and Fe dispersion of 10.1%. The maximum selectivity to C₂ through C₄ olefins was 43.0 wt.%, and the selectivity to CH₄ was low to 14.8 wt.%.     

Fischer–Tropsch synthesis on mono- and bimetallic Co and Fe catalysts supported on carbon nanotubes

An extensive study of Fischer–Tropsch synthesis (FTS) on carbon nanotubes (CNTs)-supported bimetallic cobalt/iron catalysts is reported. Up to 4 wt.% of iron is added to the 10 wt.% Co/CNT catalyst by co-impregnation. The physico-chemical properties, FTS activity and selectivity of the bimetallic catalysts were analyzed and compared with those of 10 wt.% monometallic cobalt and iron catalysts at similar operating conditions (H₂/CO = 2:1 molar ratio, P = 2 MPa and T = 220 °C). The metal particles were distributed inside the tubes and the rest on the outer surface of the CNTs. For iron loadings higher than 2 wt.%, Co–Fe alloy was revealed by X-ray diffraction (XRD) techniques. 0.5 wt.% of Fe enhanced the reducibility and dispersion of the cobalt catalyst by 19 and 32.8%, respectively. Among the catalysts studied, cobalt catalyst with 0.5% Fe showed the highest FTS reaction rate and percentage CO conversion. The monometallic iron catalyst showed the minimum FTS and maximum water–gas shift (WGS) rates. The monometallic cobalt catalyst exhibited high selectivity (85.1%) toward C₅+ liquid hydrocarbons, while addition of small amounts of iron did not significantly change the product selectivity. Monometallic iron catalyst showed the lowest selectivity for 46.7% to C₅+ hydrocarbons. The olefin to paraffin ratio in the FTS products increased with the addition of iron, and monometallic iron catalyst exhibited maximum olefin to paraffin ratio of 1.95. The bimetallic Co–Fe/CNT catalysts proved to be attractive in terms of alcohol formation. The introduction of 4 wt.% iron in the cobalt catalyst increased the alcohol selectivity from 2.3 to 26.3%. The Co–Fe alloys appear to be responsible for the high selectivity toward alcohol formation.     

Heterogeneous modeling for fixed-bed Fischer–Tropsch synthesis: Reactor model and its applications

A comprehensive one-dimensional heterogeneous reactor model is developed to simulate the performance of fixed-bed Fischer–Tropsch reactors for hydrocarbon production. The detailed mechanistic kinetics is combined into the reactor model along with considering the fact that the catalyst pores are filled with liquid wax under realistic conditions. The equilibrium between the gases in the bulk and the wax in the catalyst pores is correlated by using a modified SRK equation of state (MSRK EOS). The model is solved by using Gear method to integrate the reactor model with the embedded pellet model discretized by orthogonal collocation on finite elements. The validity of the reactor model is tested against the measured data from different-scale demonstration processes. Satisfactory agreements between model predictions and experiment results are obtained. Detailed numerical simulations are performed to investigate the effect of major process parameters on the reaction behavior of fixed-bed FTS systems with recycle operation.     

Online measurement of solids motion in fluidized bed reactor with different distributor for Fischer–Tropsch synthesis

In this paper, the distributions of particle velocity in a gas–solid fluidized bed with branched pipe distributor or circle distributor were measured by using a laser Doppler velocimetry. Our results show that, within a certain range of superficial gas velocity, when using circle distributor, the particle velocity is large and the distribution of the particle velocity is even more compared with the branched pipe distributor. On the basis of the amplitude of tangential movement statistics, the amplitude of tangential movement statistics (AVATMS) decreases with increasing the axial height under the appropriate superficial gas velocity.     

Effects of Zr and K Promoters on Precipitated Iron-Based Catalysts for Fischer–Tropsch Synthesis

Abstract  

The effects of Zr and K promoters on the structure, adsorption, reduction, carburization and catalytic behavior of precipitated iron-based Fischer–Tropsch synthesis (FTS) catalysts were investigated. The catalysts were characterized by N₂ physisorption, temperature-programmed reduction/desorption (TPR/TPD) and M?ssbauer effect spectroscopy (MES) techniques. As revealed by N₂ physisorption, Zr and/or K promoted catalysts showed lower surface area than Fe/SiO₂ catalyst. Zr promoter inhibited the reduction and carburization because of the interaction between Fe and Zr in Fe–Zr/SiO₂ catalysts. K promoter enhanced the reduction in CO and apparently facilitated the CO adsorption, thus promoted the carburization, but it retarded the reduction in H₂ and severely suppressed the H₂ adsorption. Compared with the singly promoted catalysts, the doubly promoted catalyst had the highest FTS activity. In addition, both Zr and K promoters suppressed the formation of methane and shifted the production distribution to heavy hydrocarbons.     

Co and Fe Catalysed Fischer–Tropsch Synthesis in Biofuel Production

Synthesis of liquid biofuels from synthesis gas is considered. A series of Co, Co/Ru and Fe catalysts supported by three Al₂O₃ based supports were prepared and tested for the Fischer–Tropsch (FT) reaction. The effects of supports and precursor salts on the activity of the catalysts were studied in the hydrogenation of CO using H₂/CO in a ratio of 2:1. The most active catalysts were tested with gas mixture having a composition close to synthesis gas derived by gasification of biomass. The combination of precursor salt and support is significant in order to get an active catalyst. Cobalt-based catalysts with traces of ruthenium on a small particle support proved to be the most active in the production of hydrocarbons with FT reaction.     

Effect of support and promoter on the catalytic performance and structural properties of the Fe–Co–Mn catalysts for Fischer–Tropsch synthesis

Co-precipitated Fe–Co–Mn catalysts were tested for production of light olefins via Fischer–Tropsch synthesis. The effects of different supports such as Al₂O₃, SiO₂, TiO₂ and MgO and subsequently the effect of optimum support loading and also the effect of different promoters including Li, Cs, K, Rb and Ru on the catalytic performance and structure of Fe–Co–Mn catalyst were investigated. It was found that the Fe–Co–Mn catalyst containing 10 wt% MgO has shown the better catalytic performance. Characterization of the catalyst precursors and calcined samples was carried out using XRD, SEM, EDS, BET, TPR, TGA and DSC.     

A new method of bimodal support preparation and its application in Fischer–Tropsch synthesis

A simple preparation method of bimodal silica was developed by introducing SiO₂ sol into large pores of SiO₂ gel pellet directly. Cobalt supported on this kind of bimodal silica support, exhibited remarkably high activity in liquid-phase Fischer–Tropsch synthesis, which was attributed to its bimodal structure having not only a higher surface area but also a larger pore size. The support with a large surface area allowed highly dispersed cobalt particle and its large pore size improved the diffusion of reactants and products.     

Fischer–Tropsch Synthesis on Co/Al2O3 Catalyst: Effect of Pretreatment Procedure

The effect of pretreatment procedure on catalytic performance during Fischer–Tropsch synthesis (FTS) of unpromoted cobalt on alumina (15 %Co/Al₂O₃) catalyst was studied in a fixed-bed reactor. Pure carbon monoxide or a mixture of hydrogen and carbon monoxide were used as reducing agents prior to FTS. Pretreatments with pure CO result in low activity and high selectivity to methane and gaseous hydrocarbons in comparison to standard hydrogen reduction. The use of synthesis gas (H₂/CO = 2/1) as a reducing agent resulted in high initial activity and high selectivity to gaseous hydrocarbons. Pretreatment procedure that utilized synthesis gas after the CO reduction resulted in low activity but high selectivity to high molecular weight hydrocarbons. Catalyst performance is strongly affected by the presence of cobalt carbides, cobalt oxide and/or various types of carbon species on the surface as determined by X-ray diffraction and temperature-programmed hydrogenation and oxidation characterization techniques.     

Confined Iron Nanoparticles on Mesoporous Ordered Silica for Fischer–Tropsch Synthesis

Iron oxide particles were deposited in an ordered mesoporous material (SBA-15) with the aim of studying its behavior in the catalytic hydrogenation of CO (Fischer–Tropsch Synthesis). Bulk iron oxide, and iron supported on porous silica with different textural properties (Aerosil^®-200) were used for comparison. The characterization of the materials showed that in the Fe@SBA-15 material, iron nanoparticles were confined inside the mesopores of the SBA-15 support (pore diameter ~?8 nm), and Fe@Aerosil^®-200 material also presented iron oxide nanoparticles highly dispersed on the material. In situ Synchrotron radiation XRD studies were performed in order to study the evolution of iron phases in the Fe@SBA-15 and the bulk iron oxide under hydrogen and hydrogen/carbon monoxide conditions. DFT calculations were performed on bare Fe(100) and a Fe₁₆ cluster in CO activation and C_xH_y hydrogenation. Catalytic microactivity tests, performed at conversions of ~?6–8%, showed important differences in the selectivity of the materials. Higher selectivity to methane and light hydrocarbons were observed in the supported catalysts (Fe@SBA-15 and Fe@Aerosil^®-200) than in bulk Fe catalyst. Moreover, the supported catalysts showed selectivity to ethylene (Fe@SBA-15) and propylene (Fe@Aerosil^®-200), products that were not observed in the bulk iron catalyst. On the other hand, bulk iron showed a major selectivity to higher hydrocarbons (C₅–C₉) and oxygenates.

     

Effect of support morphology and Pd promoter on Co/SBA-15 for Fischer–Tropsch Synthesis

An influence of support morphology and Pd promoter on physicochemical properties and catalytic performance of Co/SBA-15 in Fischer–Tropsch Synthesis (FTS) was investigated. SBA-15(M) from a hydrothermal synthesis with decane addition had smaller particle size, larger pore size and shorter cavity length which enhanced the dispersion of cobalt oxides, eased diffusion of reactants and improved the FTS performance. 10Co/SBA-15(M) provided the highest and most steady conversions of CO and H₂ with the highest yield of C₅–C₉ products. The addition of Pd enhanced the reduction of cobalt oxides but produced more methane and light paraffins.     

Promotion Effects of Platinum and Ruthenium on Carbon Nanotube Supported Cobalt Catalysts for Fischer–Tropsch Synthesis

Abstract  

Carbon nanotube supported nano-size monometallic and noble metal (Pt and Ru) promoted cobalt catalysts were prepared by incipient wetness impregnation (IWI) using solution of cobalt nitrate and characterized by nitrogen adsorption isotherm, X-ray diffraction (XRD), temperature programmed reduction, in situ magnetic method and TEM. Analysis of the magnetization and H₂-TPR data suggested promotion with platinum and ruthenium significantly decreased the cobalt species reduction temperature. TEM and XRD results showed that the presence of noble metal promoters had no significant effect on the size of cobalt for carbon naotube as catalytic support. Promotion of cobalt carbon nanotube-supported catalysts with small amounts of Pt and Ru resulted in slight increase in Fischer–Tropsch cobalt time yield. The Pt and Ru promoted cobalt catalyst exhibited carbon monoxide conversion of 37.1 and 31.4, respectively. C₅+ hydrocarbon selectivity was attained at 80.0%. The Pt promoted cobalt supported on carbon nanotube yielded better catalytic stability than that of the monometallic cobalt catalyst.