Fischer-Tropsch (F-T) synthesis converts syngas to liquid fuels. However, the reaction products of traditional F-T synthesis follow the Anderson-Schulz-Flory (ASF) distribution law, and the resulting carbon number distribution is wide and complex with a high content of heavy hydrocarbons. This makes it difficult to concentrate the carbon number of liquid hydrocarbons to within a specific range.
A team at Zhejiang University in China has investigated the influence of rare-earth metal ions promotion on the F-T synthesis of gasoline-range hydrocarbons (GRHs, C5–C12 hydrocarbons). In a paper in the journal Fuel, they report that a Co/Y-β catalyst exhibited optimal GRHs selectivity of 49% with a yield of 41.4% at 260 °C, 2 MPa, H2/CO = 2, and 1,064 h−1.
To increase the proportion of gasoline-range hydrocarbons (GRHs) from F-T synthesis, some researchers have regulated the structures and properties of catalysts by introducing supports rich in acid sites or adding metal promoters to enhance the in situ hydrocracking reaction of long-carbon-chain hydrocarbons and the isomerization of linear hydrocarbons.
In recent years, the use of bifunctional catalysts combining acidic zeolites with active components has become a promising means of achieving selective F-T synthesis. … H-β zeolite has been widely utilized in selective F-T synthesis as it shows high cracking activity and selectivity for middle distillates on account of its distinct pore structure and acidity. … Many researchers have found that the introduction of a small amount of a rare-earth metal in conventional F-T synthesis catalysts can promote the degree of reduction, catalytic performance and lifetime.
… In this study, H-β acidic zeolite has been modified by these typical rare-earth metal ions (Y3+, Ce3+ and La3+), prior to the introduction of cobalt nanoparticles by a wet-impregnation method. The resultant Co-based catalysts have been applied for selective F-T synthesis to study the influence of modification with these cations on the structure and physicochemical properties. Moreover, the effect of different rare-earth ion-exchange modifications on the catalytic activity and products of F-T synthesis are discussed to gain insight into how the selectivity for the target products might be improved.—Zhuo et al.
The researchers found that the modification of Y3+ and Ce3+ on Co/H-β enhanced the activity and stability of the catalyst. Additionally, modification with rare-earth metal ions enhanced the strength of the CO-metal bond while weakening that of C-O bond, leading to an increase in selectivity for GRHs and stability.
The doping of Y promoted the dispersion of active Co particles, and the addition of Ce3+ strengthened the reducibility of Co/H-β, thus facilitating the conversion of CO.
We hope that this work will be helpful for further researches on the efficient regulation of selective F-T synthesis for more GRHs, as well as in-depth understanding of the effect of unique ion-exchange modified methods on the structure and physicochemical properties of the modified catalysts.—Zhuo et al.
Yexin Zhuo, Lingjun Zhu, Jiacheng Liang, Shurong Wang (2020) “Selective Fischer-Tropsch synthesis for gasoline production over Y, Ce, or La-modified Co/H-β,” Fuel, Volume 262, 116490 doi: 10.1016/j.fuel.2019.116490