Bifunctional Co‐based Catalysts for Fischer‐Tropsch Synthesis: Descriptors Affecting the Product Distribution

Abstract

The conversion of synthesis gas to hydrocarbons in the Fischer‐Tropsch (FT) synthesis suffers from a broad product distribution not directly providing high fuel quality. This work, therefore, aims at bifunctional catalysts combining the FT and hydroprocessing (HP) reaction for tailoring the product spectrum. Therefore, we applied a bottom‐up synthesis strategy for bifunctional cobalt/zeolite catalysts and investigated the obtained materials by advanced characterizations such as 3D TEM tomography. Based on the results, descriptors are defined for the acidity and the porosity, which are varied by changing the material preparation parameters. The catalytic properties of the obtained materials are studied in FT experiments at industrially relevant conditions (20 bar, 240 and 260 °C) and are correlated to the material properties by means of the respective descriptors. Therefore, the product distribution was analyzed in detail and distinguished between n‐paraffins and 1‐olefins as typical FT‐products as well as paraffinic and olefinic isomers formed in the HP classified in different fractions. It was found that, apart from the acidity, the pore structure plays a vital role in primary and secondary cracking/isomerization reactions. In addition to that, the particular 3D pore structure and thus the individual transport trajectories of the FT products are strongly affecting the cracking and isomerization probability and consequently the product distribution.

Cobalt‐based Nanoreactors in Combined Fischer‐Tropsch Synthesis and Hydroprocessing: Effects on Methane and CO2 Selectivity

“…However, it is reasonable considering the improved WGS activity provided by the presence of cobalt oxide species as discussed above. For a more detailed discussion of the product distribution for Co@mSiO 2 , Co@silicalite‐1, and Co@HZSM5 we refer to our recent work [15] …”

“…In industrial applications mainly long‐chain paraffins and a low methane selectivity are desired, while the long‐chain paraffins are subsequently hydrocracked over zeolite catalysts in a second reactor at temperatures between 250 and 350 °C to yield short‐chain hydrocarbons for the use as liquid fuel [10] . The combination of a FT catalyst and an active material for hydroprocessing (HP) in one single reactor requires a compromise between the optimal conditions for each reaction but is currently widely discussed in scientific literature with remarkable success [9,11,15] . Different concepts are for example the usage of catalyst layers [10,16] or physical mixtures [10,11,16] as well as the impregnation of zeolites [13,17,22] as support materials.…”

Insights into Fischer–Tropsch catalysis: current perspectives, mechanisms, and emerging trends in energy research

“…They also report that Co/H-Y-meso catalysts with Brønsted acid sites have more C4-C5 products caused by higher isomerization and cracking activities, while the Co/Y-meso-Na catalyst without Brønsted acid sites has more CH 4 and C10-C15 due to a high hydrogenolysis activity (Peng et al, 2015). The pore structure of the catalyst requires particular emphasis (Straß-Eifert et al, 2021). also showed that Co/Y-meso-Na could effectively crack C21+ hydrocarbons and that Co/Y-micro-Na catalysts with a different pore structure than the CO/Y-meso-Na have higher CH 4 and C2-C4 selectivity.…”

CO2 Conversion by Fischer‐Tropsch Synthesis Using Na‐Modified Fe Catalysts

“…While MtG primarily leads to gasoline components with substantial fractions of aromatics, FTS provides a broad spectrum of linear alkenes and alkanes covering gasoline, kerosene, diesel and fuel oil components, and waxes. It has been shown that the yield of fuel components can be increased by combining FTS with a cracking catalyst in the same reactor unit [8][9][10]. Special reactor concepts such as microchannel reactors can also be used to alter the FTS product spectrum [11].…”