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

Abstract

The hydrogenation of CO and CO 2 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 CO 2 using a zinc-and sodiumpromoted iron catalyst (FeZnNa catalyst) are carefully investigated in this work. For CO 2 hydrogenation, ethylene showed negligible impact on CO 2 conversion, CO selectivity, or CH 4 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 CO 2 hydrogenation. Structural analysis using XRD and Mossbauer spectroscopy revealed that the catalyst in CO 2 hydrogenation consisted exclusively of the Fe 5 C 2 phase, whereas CO hydrogenation resulted in the formation of both Fe 5 C 2 and Fe 2 C phases. XPS and TPO analyses indicated significantly lower carbon deposition on the catalyst during CO 2 hydrogenation compared to that during CO hydrogenation.