Linear α-olefin production with Na-promoted Fe-Zn catalysts via Fischer-Tropsch synthesis.

The production of linear alpha-olefins (α-olefins) is a practical way to increase the economic potential of the Fischer-Tropsch synthesis (FTS) because of their importance as chemical intermediates. Our study aimed to optimize Na-promoted Fe1Zn1.2O x catalysts such that they selectively converted syngas to linear α-olefins via FTS at 340 °C and 2.0 MPa. The Fe1Zn1.2O x catalysts were calcined at different temperatures from 350 to 700 °C before Na anchoring. The increase in the size of the ZnFe2O4 crystals comprising the catalyst had a negative effect on the reducibility of Fe oxides and the particle size of Fe5C2 during the reaction. The Na species in the catalyst restrained the reduction of Fe1Zn1.2O x but facilitated the formation of Fe5C2. When pure Fe1Zn1.2O x was calcined at 400 °C, the corresponding catalyst (i.e., Na0.2/Fe1Zn1.2O x (400)) exhibited higher catalytic activity and stability than the other catalysts for a 50 h reaction. Compared to the other catalysts, Na0.2/Fe1Zn1.2O x (400) enabled a higher number of active Fe carbides (Fe5C2) to intimately interact with the Na species, even though the catalyst had a lower total surface basicity based on surface area. The Na0.2/Fe1Zn1.2O x (400) showed a maximum hydrocarbon yield of 49.7% with a maximum olefin selectivity of 61.3% in the C1-C32 range. Examination of the reaction product mixture revealed that the Na0.2/Fe1Zn1.2O x catalysts converted α-olefins to branched paraffins (13.9-19.5%) via a series of isomerization, skeletal isomerization, and hydrogenation reactions. The Na0.2/Fe1Zn1.2O x (400) catalyst had a relatively low consumption rate of internal olefins compared to other catalysts, resulting in the lowest selectivity for branched paraffins. The Na0.2/Fe1Zn1.2O x (400) showed a maximum α-olefin yield (26.6%) in the range C2-C32, which was 27.9-50.0% higher than that of other catalysts. The α-olefin selectivity in the C5-C12 range for the Na0.2/Fe1Zn1.2O x (400) was 37.5% relative to the total α-olefins.

Efficient utilization of greenhouse gases in a gas-to-liquids process combined with CO2/steam-mixed reforming and Fe-based Fischer-Tropsch synthesis.

Two process models for carbon dioxide utilized gas-to-liquids (GTL) process (CUGP) mainly producing light olefins and Fischer-Tropsch (F-T) synthetic oils were developed by Aspen Plus software. Both models are mainly composed of a reforming unit, an F-T synthesis unit and a recycle unit, while the main difference is the feeding point of fresh CO2. In the reforming unit, CO2 reforming and steam reforming of methane are combined together to produce syngas in flexible composition. Meanwhile, CO2 hydrogenation is conducted via reverse water gas shift on the Fe-based catalysts in the F-T synthesis unit to produce hydrocarbons. After F-T synthesis, the unreacted syngas is recycled to F-T synthesis and reforming units to enhance process efficiency. From the simulation results, it was found that the carbon efficiencies of both CUGP options were successfully improved, and total CO2 emissions were significantly reduced, compared with the conventional GTL processes. The process efficiency was sensitive to recycle ratio and more recycle seemed to be beneficial for improving process efficiency and reducing CO2 emission. However, the process efficiency was rather insensitive to split ratio (recycle to reforming unit/total recycle), and the optimum split ratio was determined to be zero.

Ordered mesoporous carbon nanochannel reactors for high-performance Fischer-Tropsch synthesis.

A hexagonally ordered mesoporous carbon, CMK-3, was utilized as a support for a Fischer-Tropsch catalyst. Each array of elongated pore structures with Co nanoparticles can be regarded as a nanochannel reactor. Due to the pore confinement and the hydrophobic nature of the support, this catalyst demonstrated excellent catalytic performance.

Ordered mesoporous tungsten suboxide counter electrode for highly efficient iodine-free electrolyte-based dye-sensitized solar cells.

A disulfide/thiolate (T(2)/T(-)) redox-couple electrolyte, which is a promising iodine-free electrolyte owing to its transparent and noncorrosive properties, requires alternative counter-electrode materials because conventional Pt shows poor catalytic activity in such an electrolyte. Herein, ordered mesoporous tungsten suboxide (m-WO(3-x)), synthesized by using KIT-6 silica as a hard template followed by a partial reduction, is used as a catalyst for a counter electrode in T(2)/T(-)-electrolyte-based dye-sensitized solar cells (DSCs). The mesoporous tungsten suboxide, which possesses interconnected pores of 4 and 20 nm, provides a large surface area and efficient electrolyte penetration into the m-WO(3-x) pores. In addition to the advantages conferred by the mesoporous structure, partial reduction of tungsten oxide creates oxygen vacancies that can function as active catalytic sites, which causes a high electrical conductivity because of intervalence charge transfer between the W(5+) and W(6+) ions. m-WO(3-x) shows a superior photovoltaic performance (79 % improvement in the power conversion efficiency) over Pt in the T(2)/T(-) electrolyte. The superior catalytic activity of m-WO(3-x) is investigated by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization curve analysis.

Efficient utilization of greenhouse gas in a gas-to-liquids process combined with carbon dioxide reforming of methane.

A process model for a gas-to-liquids (GTL) process mainly producing Fischer-Tropsch (FT) synthetic oils has been developed to assess the effects of reforming methods, recycle ratio of unreacted syngas mixture on the process efficiency and the greenhouse gas (GHG) emission. The reforming unit of our study is composed of both steam reforming of methane (SRM) and carbon dioxide reforming of methane (CDR) to form syngas, which gives composition flexibility, reduction in GHG emission, and higher cost-competitiveness. With recycling, it is found that zero emission of CO(2) from the process can be realized and the required amount of natural gas (NG) can be significantly reduced. This GTL process model has been built by using Aspen Plus software, and it is mainly composed of a feeding unit, a reforming unit, an FT synthesis unit, several separation units and a recycling unit. The composition flexibility of the syngas mixture due to the two different types of reforming reactions raises an issue that in order to attain the optimized feed composition of FT synthesis the amount of flow rate of each component in the fresh feed mixture should be determined considering the effects of the recycle and its split ratio. In the FT synthesis unit, the 15 representative reactions for the chain growth and water gas shift on the cobalt-based catalyst are considered. After FT synthesis, the unreacted syngas mixture is recycled to the reforming unit or the FT synthesis unit or both to enhance process efficiency. The effect of the split ratio, the recycle flow rate to the FT reactor over the recycle flow rate to the reforming unit, on the efficiency of the process was also investigated. This work shows that greater recycle to the reforming unit is less effective than that to the FT synthesis unit from the standpoint of the net heat efficiency of the process, since the reforming reactions are greatly endothermic and greater recycle to the reformer requires more energy.