(632e) Enhancing Light Olefin Production from Syngas Via Indium-Promoted Iron Catalysts

Light olefins, specifically C₂ to C₄ olefins, are essential building blocks for a variety of chemicals, including polymers, pharmaceuticals, and solvents. Conventionally, these olefins are primarily obtained through the catalytic cracking of large alkanes at high temperatures and the dehydrogenation of light alkanes found in natural gas. However, with dwindling oil reserves, there is a pressing need for alternative methods of light olefin production. Fischer-Tropsch synthesis (FTS) offers a viable way to produce light olefins by utilizing synthesis gas (syngas). To optimize the FTS 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 methane formation. Additionally, it is vital to regulate the activation of CO on the catalyst surface to minimize CO₂ production.

In this study, a series of alumina-supported In-promoted Fe catalysts (with Fe:In loading ratios of 20:1, 10:1, and 20:3) were examined to determine how to control catalytic activity and selectivity during syngas conversion to light olefins. Pure Fe metal on alumina was also studied for comparison. The In-promoted Fe catalyst (10 mol % In based on Fe) demonstrated high selectivity (45% including CO₂) and remarkable stability (72-hour run) in converting syngas (2:1 H₂/CO ratio) to olefins, with a 10% CO conversion at 400°C and 5 bar. The results suggest that the ensemble size of Fe sites, catalyst surface reactivity, and surface Fe electronic structure can be systematically adjusted as a function of Fe:In loading ratios. These findings are supported by performance studies, in-situ CO temperature programmed desorption (TPD) studies, XPS analysis, and Steady State Isotopic Transient Kinetic Analysis (SSITKA). Indium-promoted iron catalysts hold potential for facilitating efficient syngas conversion, derived from biogas and landfill gas reforming, into olefins, offering a sustainable alternative to crude oil cracking.