Carbon Dioxide Hydrogenation under Subcritical and Supercritical Conditions in the Presence of 15% Fe/SiO2 Catalyst

Results are presented from a comparative study of CO2 hydrogenation under gas-phase and supercritical conditions for CO2 in the presence of 15% Fe/SiO2 catalyst. The reaction is studied in the temperature range of 300–500°C at atmospheric pressure under gas-phase conditions and at a pressure of 95 atm under supercritical conditions at an Н2 : СО2 molar ratio of 2 : 1. It is found that the process proceeding under supercritical conditions lowers CO selectivity from 90–95 to 30–50% over the range of temperatures and raises (up to 60%) the hydrocarbon selectivity. In contrast to gas-phase hydrogenation, the formation of alcohols is observed in the reaction under supercritical conditions. Using a combination of thermogravimetry, differential thermogravimetry, and differential thermal analysis (TG–DTG–DTA), it is shown that the process proceeding under supercritical conditions results in a 2.2-fold drop in the amount of carbon-like deposits on the catalyst surface. X-ray diffraction analysis shows that under gas-phase process conditions, graphite-like structures form on the catalyst surface; this effect is not observed under supercritical conditions. The developed catalyst and the process for CO2 hydrogenation can be recommended for the further modification and improvement of the properties of a catalyst based on iron nanoparticles that is much (10–100 times) cheaper than the previously reported CO2 hydrogenation catalysts.