Effect of Carbon Supports on Supercritical Hexane Mediated, Fe-Catalyzed Fischer-Tropsch Synthesis

Abstract

The Fischer-Tropsch synthesis (FTS) process consists of surface-catalyzed reactions that collectively convert syngas into hydrocarbons, oxygenates, CO2, water, and heat. In this work, five Fe-based, carbon-supported catalysts were synthesized, characterized, and evaluated for FTS reaction performance. Carbon supports consisted of large-diameter multi-walled carbon nanotubes (MWNTs), small-diameter MWNTs, carbon nanofibers, and graphene nanoplatelets and each catalyst was tested under both gas phase and supercritical reaction conditions to more thoroughly interrogate their behavior.

All of the carbon-supported catalysts were highly active relative to a more traditional precipitated catalyst, but wide variations in conversion, CO2 selectivity, propagation probability, and product functionality between catalysts make it clear that that carbon support structure can significantly impact FTS catalyst performance. Of the catalysts studied, the K-promoted catalyst supported on large-diameter MWNTS had the most unique behavior, producing long-chain aldehydes under both gas phase and supercritical reaction conditions. This production and extraction of significant quantities of aldehydes in Fe-catalyzed, gas phase FTS is unprecedented in the literature, where such behavior is limited to slurry phase or supercritical conditions. In the larger context of the catalyst’s behavior, this unique result also serves as significant evidence that an oxygenate-based mechanism is active in product formation in Febased FTS.