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.