Unraveling the complex interactions between structural features and reactivity of iron-based catalysts across various supports in the synthesis of light olefins from syngas

Abstract

This study provides a systematic examination of the hydrogenation of CO over mixed Fe-Co-K catalysts on SiO₂, TiO₂, and Al₂O₃ supports for the production of light olefins. The unsupported FeCo/K catalyst, while demonstrating selectivity towards light olefins, yielded a low space–time yield (STY) for hydrocarbon formation. Additionally, the Fe₃O₄ phase in the spent catalyst appeared to promote an increased rate of CO₂ formation. The SiO₂-supported catalyst showed a high dispersion of isolated Fe particles but were less effective in synthesizing light olefins. The interaction of Fe species with TiO₂ support was found to be strong, impeding the formation of the active Fe₅C₂ phase and thus lowering the yield of light olefins. Al₂O₃ stood out as the most effective support, ensuring an optimal dispersion of the Fe phase with minimal interaction, enabling the Fe to effectively synergize with K. This synergy promoted the formation of the iron carbide Fe₅C₂ phase, essential for efficient CO hydrogenation to light olefins, and achieved a notable STY of 17.2 mmol gcat ⁻¹h⁻¹ at 360 °C and 20 bar. Long-term stability testing underscored the influence of reaction temperature on light olefins yield, with paraffin wax formation at 300 °C leading to catalyst deactivation through adsorption and accumulation. Conversely, at 360 °C, a distinct carbon layer was observed, forming an extended structure that did not directly cover the catalyst's surface. These findings contribute valuable knowledge for the custom development of catalysts tailored for light olefins production from syngas, offering a promising avenue for future research.