New mechanism insight for the hydrogenation of CO/CO2 gas mixtures to hydrocarbons over iron-based catalyst

Sandeep Badoga,Michela Martinelli,Muthu Kumaran Gnanamani,Young Koh,Wilson D Shafer

doi:10.1016/j.catcom.2021.106284

Sandeep Badoga, Michela Martinelli + Show 3 more

Open Access

https://doi.org/10.1016/j.catcom.2021.106284

Copy DOI

Abstract

Iron-based catalysts are the most suitable candidates for converting CO2 or CO2-rich syngas to hydrocarbons. However, several issues about the mechanism of CO2 hydrogenation are still unclear. In this work, we investigated the performance of an iron-based catalyst with H2/CO2, H2/CO/N2 and H2/CO/13CO2/N2 gas mixtures at the same process conditions (T = 270°C, P = 175 psi and SV = 3 NL/h/gcat). The CO2 hydrogenation rate was much lower than that observed for CO hydrogenation. 13CO2 tracer experiments indicated that CO2 is hydrogenated to hydrocarbons via the reverse water-gas shift even when present in small concentration (1.8 vol%). 13C enrichment was observed in both CO and C1-C4 hydrocarbons.

Highlights

Fischer-Tropsch Synthesis (FTS) converts synthesis gas (CO and H2) from various carbon-containing feedstocks to hydrocarbons
The CO2 hydrogenation rate was much lower than that observed for CO hydrogenation. 13CO2 tracer experiments indicated that CO2 is hydro genated to hydrocarbons via the reverse water-gas shift even when present in small concentration (1.8 vol%). 13C enrichment was observed in both CO and C1-C4 hydrocarbons
A general agreement is that CO2 can only be hydrogenated at low CO partial pressures, while different results are reported about the effect on the CO conversion rate and product dis tribution when CO2 is cofed [6,7,10,15,19,20]

Summary

Introduction

Fischer-Tropsch Synthesis (FTS) converts synthesis gas (CO and H2) from various carbon-containing feedstocks (i.e., natural gas, coal, and biomass) to hydrocarbons. Iron-based catalysts are reported to be more effective than cobalt for converting CO2 and CO/CO2 gas mixtures to long-chain hydrocarbons [6,7,8,9,10,11,12,13]. This is mostly attributed to their intrinsic activity for the reverse water-gas shift (RWGS) reaction [6,9,10]. A state-of-the-art iron-based catalyst was tested at representative FTS process conditions for the hydrogenation of CO/CO2 gas mixtures. A state-of-the-art iron-based catalyst was tested at representative FTS process conditions for the hydrogenation of CO/CO2 gas mixtures. 13Clabelled CO2 was cofed during CO hydrogenation in order to have further insights on the mechanism at hand

Experimental

CO and CO2 hydrogenation

Conclusions