(387e) Cesium-Promoted Iron Catalysts for Selective Hydrogenation of CO to Light Olefins

Light olefins such as ethene, propene, and butene are crucial building blocks chemicals for the modern chemical industry utilized in various products such as polymers, detergents, adhesives, and pharmaceuticals. The supply needs to catch up for these critical chemicals to address a growing gap of 4.7% per year. Hydrogenation of CO and CO₂ into olefins through Fischer-tropsch synthesis (FTS), is a promising approach for sustainable production to meet the olefin gap. To optimize the C=O hydrogenation process, it is crucial to precisely control the affinities of carbon and hydrogen on the catalyst surface, promoting C-C coupling for olefin products while preventing over-hydrogenation and C1 formation. The controlled synthesis of Fe-phases that are active and selective towards C2+ hydrocarbons is also crucial to achieving this goal.

In this work, a series of cesium-promoted Fe was explored for the hydrogenation of CO into C₂=C₄ olefins, examining control on catalytic activity and selectivity. Unpromoted Fe was studied as a comparison. The Cs-promoted Fe catalyst (20 mol % K based on Fe) demonstrated high selectivity and remarkable stability (110-hour run) in converting CO to olefins (45% C₂=C₄ selectivity), at ~20% CO conversion at 400°C and 5 bar. Our results suggests that ensemble size of Fe sites, catalyst surface reactivity, and surface Fe electronic structure can be systematically adjusted as a function of Fe and Cs loading ratios. The catalyst bulk structure was studied using XRD, Mössbauer spectroscopy, and TEM, while In-situ temperature-programmed reactions studies, XPS, and Energy Loss Near Edge Structure (ELNES) analysis elucidate the electronic interaction. Steady State Isotopic Transient Kinetic Analysis (SSITKA) and Chemical Transient Kinetics (CTK) reveal the mechanism of promotion and surface kinetics of CO hydrogenation. This work demonstrates promoted Fe-catalyst as effective catalyst for sustainable production of light olefins from syngas.