Comparative Study on the Effect of Ethylene Cofeeding in CO₂ and CO Hydrogenation to Olefins over FeZnNa Catalyst

The hydrogenation of CO and CO2 to long-chain olefins presents a promising route for chemical production, but optimizing the reaction process requires a thorough understanding of the tail gas recycling process. The effects of cofeeding ethylene on the hydrogenation of CO and CO2 using a zinc- and sodium-promoted iron catalyst (FeZnNa catalyst) are carefully investigated in this work. For CO2 hydrogenation, ethylene showed negligible impact on CO2 conversion, CO selectivity, or CH4 selectivity but primarily served as a feedstock for the production of ethane and higher carbon number olefins. In contrast, during CO hydrogenation, CO conversion improved with ethylene cofeeding. Ethylene also contributed to chain growth, although a higher fraction was converted to ethane via hydrogenation compared to CO2 hydrogenation. Structural analysis using XRD and Mössbauer spectroscopy revealed that the catalyst in CO2 hydrogenation consisted exclusively of the Fe5C2 phase, whereas CO hydrogenation resulted in the formation of both Fe5C2 and Fe2C phases. XPS and TPO analyses indicated significantly lower carbon deposition on the catalyst during CO2 hydrogenation compared to that during CO hydrogenation.