Increased CO2 hydrogenation to liquid products using promoted iron catalysts

Abstract

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.