Increased CO2 hydrogenation to liquid products using promoted iron catalysts

• Published in: Journal of catalysis Vol. 369; pp. 239 - 248
• Main Authors: Shafer, Wilson D., Jacobs, Gary, Graham, Uschi M., Hamdeh, Hussein H., Davis, Burtron H.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.01.2019
• Subjects: Activity; Alkali promoter; CO2 hydrogenation; Iron-based catalysts; Product selectivity; Product selectivity; Activity; Iron-based catalysts; CO2 hydrogenation; Alkali promoter
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2018.11.001

Note: These runs were under the same conditions (i.e. temperature, pressure SV etc.), sampled with the same time-on-stream and utilized the same amount of startup solvent. Thus, runs under the same activity displayed the same levels of start-up solvent. [Display omitted] •Rb and Cs promoted iron catalysts were superior to the K promoted iron catalyst.•The initial overall CO2 conversion is much higher for Cs and Rb.•These catalysts had a much higher selectivity toward C5+ materials.•A synergistic effect for Rb and Cs promoters yield cheaper superior catalysts.•Degradation of these catalysts are mainly through coking, not oxidation. The effect of alkali promoter (K, Rb and Cs) on the performance of precipitated iron-based catalysts was investigated for carbon dioxide (CO2) hydrogenation. Characterization by temperature-programmed reduction with CO, Mössbauer spectroscopy, and transmission electron microscopy were used to study the effect of alkali promoter interactions on the carburization and phase transformation behavior of the catalysts. Under similar reaction conditions, cesium (Cs) and rubidium (Rb) promoted catalysts exhibited the highest initial CO2 conversions to higher hydrocarbons. CO2 conversions then decreased to reach steady state conversions around 170 h on stream. At steady state conversion, all three catalysts exhibited similar CO2 conversions and selectivities. For comparison, a lower loaded Cs (1.5 Cs) promoted iron-based catalyst was prepared. It exhibited slightly lower initial conversion than the higher loaded Cs catalyst, but remained very stable. Among all the catalysts at steady state conversion, the 1.5 Cs promoted catalyst exhibited the highest stability. Results indicate a synergistic effect brought on by these promoters that, if balanced, could potentially yield superior CO2 hydrogenation catalysts.