A. S. Lyadov

Carbon Spheres Prepared by Hydrothermal Synthesis—A Support for Bimetallic Iron Cobalt Fischer–Tropsch Catalysts

Carbon spheres (CSs) synthesised by the hydrothermal approach were explored as a model support material for a bimetallic Fe–Co Fischer–Tropsch (FT) catalyst. The CSs were characterised by N2 adsorption–desorption, thermogravimetric analysis, FTIR spectroscopy and powder XRD. If annealed at 900 °C for 4 h, the CSs exhibited an improved surface area, thermal stability and crystallinity. A series of Fe–Co bimetallic FT catalysts supported on the annealed CSs were prepared by co‐precipitation. A variety of Fe‐to‐Co ratios were used with the total metal loadings maintained at 10 %. Catalyst reducibility studies were performed by H2 temperature‐programmed reduction and in situ powder XRD. Catalysts with a Fe/Co ratio of 5:5 (w/w) showed Co–Fe alloy formation upon reduction at >450 °C. Interestingly, the presence of this alloy did not correlate with high C5+ selectivities during FT synthesis; rather the Co‐rich/Fe‐poor catalyst gave the best selectivity. The CSs allowed the metal–metal interactions in the bimetallic systems to be monitored because of the weak interaction of the metals with the support.

Fischer-Tropsch synthesis in a three-phase system with iron catalyst nanoparticles

The features of the Fischer-Tropsch synthesis in the presence of 100Fe: 8Al2O3: 3K2O (parts by weight) catalyst nanoparticles under the slurry reactor conditions have been studied. The catalyst is prepared in situ and activated in the reactor. It has been found that during the preparation process, the catalyst reacts with the dispersion medium to form a structured system that is not liable to sedimentation. It is shown that the use of CO as a reducing agent makes it possible to increase the yield of liquid hydrocarbons by a factor of 1.5. An increase in the syngas pressure has almost no effect on the yield of liquid hydrocarbons; however, it gives the possibility of enhancing the catalyst efficiency up to 700 g/(kg Fe · h) at 40 atm. In conditions of a three-phase system, gasoline-fraction hydrocarbons, half of which consist of olefins, are mostly formed on the nanosized catalyst.

Fischer-Tropsch process in a three-phase system over iron-cobalt catalyst nanoparticles in situ synthesized in a hydrocarbon medium

It has been shown that Fe-Co nanocatalysts in situ synthesized in a hydrocarbon medium with a Fe/Co weight ratio of 2–6 can mediate the Fischer-Tropsch synthesis in a three-phase system at a pressure of 20 atm, a temperature of 250–300°C, and a CO/H2 ratio of 1: 1. The introduction of CO leads to a significant increase in the total activity of the catalyst system (KCO reaches 85% at 300°C). However, gas evolution is enhanced and the highest yield of liquid products is as low as 74 g/m3 in this case. The introduction of K and Al into the Fe-Co catalysts and the optimization of the Fe/Co ratio make it possible to increase the yield of liquid products to 143 g/m3 (Fe/Co = 2.4) and achieve an efficiency of 337 g/(kg Me h). The Fe-Co nanocatalysts exhibit a high polymerizing activity (Schulz-Flory alpha is higher than 0.8). Hydrocarbons obtained over Fe-Co-K-Al catalysts contain more than 20% olefins. Their amount increases with the increasing Fe concentration in the sample. Oxygenates formed over these catalysts are composed of alcohols by over 90%, of which ethanol prevails (65–70%).

Fischer-Tropsch synthesis in a slurry reactor in the presence of nanosized cobalt catalysts synthesized in situ in a hydrocarbon medium

Fischer-Tropsch synthesis in a slurry reactor at a pressure of 20 atm and a temperature of 220–300°C in the presence of 100Co : 2Pd : (5–50)Al2O3 and 100Co : 2Pd : (20–50)ZrO2 (parts by weight) catalysts in situ synthesized in a hydrocarbon medium has been studied. The catalysts were prepared by the decomposition of cobalt salts and promoters in melted petroleum paraffin P-2 at 300°C and in situ reduced with hydrogen. It has been found that the nanocatalyst containing 20 parts by weight of ZrO2 exhibits the highest activity in the Fischer-Tropsch synthesis and provides the yield of liquid products of 70 g/m3 at a CO conversion of 80%.

Formation of alcohols on nanosized iron catalysts under Fischer-Tropsch synthesis conditions

Regularities of the alcohol formation in a three-phase system in the presence of the nanosized 100Fe: 8Al2O3: 3K2O (parts by weight) iron catalyst under the Fischer-Tropsch synthesis conditions have been determined. It has been found that the molecular-weight distribution of alcohols does not follow the Anderson-Schulz-Flory law. The principal product is ethanol; its proportion in the mixture can be as high as 78 wt %. It has been supposed that the formation of alcohols can follow the mechanism including the CO insertion in the metal-carbon bond. It has been shown that the highest ethanol yield (78 wt %) is obtained using 20 atm, 300°C, and H2/CO = 2.5 (mol/mol), an iron-containing catalyst charge in the reactor of 2 wt %.

Synthesis of nanosized iron(III) oxide and study of its formation features

Nanosized iron(III) oxide has been obtained by thermolysis of iron(III) acetylacetonate using diphenyl ether as a dispersion medium. It has been shown that increase in thermolysis temperature from 180 to 250°C allows one to half the average size of Fe2O3 nanoparticles. The introduction of surfactant into dispersion medium also leads to decrease of the average size of particles down to 4 nm. The phase composition of the prepared nano-Fe2O3 has been established, the possibility to reduce nano-Fe2O3 into iron metal has been shown by temperature-programmed reduction

Peculiarities of the iron reduction mechanism in Fe-Al-K system

Temperature-programmed reduction was used in combination with measurements of magnetization to determine the peculiarities of iron reduction in the Fe-K-Al system. It was found that reduction by hydrogen proceeds with the formation of metallic iron through the stage of magnetite formation (Fe3O4); the effective activation energies are 63 and 39 kJ/mol for the I and II stages, respectively. It was shown that substituting carbon oxide for hydrogen leads to iron reduction proceeding only to the stage of magnetite formation (EFe3O4 = 94 kJ/mol). The magnetite interacts with CO to produce carbide (presumably Hegge carbide Fe2C). Iron reduction in the synthesis gas occurs with the preferential participation of hydrogen or carbon dioxide, depending on the rate of temperature rise.

Synthesis of tungsten sulfide nanoparticles and their tribological properties as additives for lubricating oils

Tetrathiotungstates with different alkyl groups have been synthesized by an exchange reaction between ammonium tetrathiotungstate and tetraalkylammonium halides. Synthesized samples are analyzed by elemental analysis and optical and thermal methods. Nano-WS3 particles that are stable and soluble in nonpolar hydrocarbons are prepared by thermolysis of alkyltetrathiotungstates. The average particle size of nano-WS3 is about 10–100 nm and depends on the nature of raw tetraalkylammonium halides. It is shown that nanoparticles of WS3 are soluble in Vaseline oil (1–2 wt %) and exhibit antiwear activity.

Synthesis of alcohols from CO and H2 on iron catalysts containing carbon fiber

It was found that alcohols can be synthesized from CO and H2 at 3 MPa and 280–300°C in the presence of Fe catalysts containing an activated fibrous carbon material (AFCM) as a support. It was established that 20% Fe/AFCM catalysts possess an extremely high specific activity in the conversion of carbon monoxide (∼1 × 10−4 mol CO (mol Fe)−1 s−1), which is higher than the activity of traditional bulk iron catalysts by almost an order of magnitude. The values of CO conversion and selectivity for alcohols obtained for these catalysts are close to the parameters of industrial processes (Synol process, Oxyl process, and synthesis according to Bashkirov); however, they are obtained under milder conditions in a single run rather than with the use of a recycle. The Fe/AFCM catalysts make it possible to obtain monohydric alcohols in yields to ∼50 g/m3 (to a 50% concentration in synthesis water) upon the almost complete conversion of CO. In this case, the fraction of C2-C4 alcohols was as high as 55–60%.

Fischer-tropsch iron catalysts supported on fibrous carbon material

Iron catalysts supported on an activated fibrous carbon material (AFCM) and characterized by high performance in the hydrocarbon synthesis from CO and H2 have been studied. It has been shown that the promotion of Fe/AFCM catalysts with potassium and aluminum oxides or with copper reduces the optimum temperature of Fischer-Tropsch synthesis and enhances the polymerizing activity of the catalysts.