Operando DRIFT and In situ Raman Spectroscopic Studies on Aspects of CO<sub>2</sub> Fischer‐Tropsch Synthesis Catalyzed by Bulk Iron Oxide‐Based Catalysts
Jana Weiß, Qingxin Yang, Ursula Bentrup, Evgenii V. Kondratenko, Angelika Brückner, Christoph Kubis
Abstract
Abstract Hematite is a suitable precursor to obtain catalytically active iron (oxide) phases for CO 2 Fischer‐Tropsch synthesis after a reductive pretreatment. As concluded from in situ Raman spectroscopy, in hydrogen atmosphere the transformation from α‐Fe 2 O 3 to Fe 3 O 4 is faster than the further reduction from Fe 3 O 4 to Fe (metallic iron). The rate of these steps highly depends on the temperature. Starting from pure hematite, surface formate species are formed at a CO 2 /H 2 gas mixture at elevated temperatures, observable by DRIFT‐spectroscopy. The exposure to CO 2 and CO led to surface carbonate‐carboxylate surface species. Reduced samples with varying contents of Fe 3 O 4 and Fe did not show any observable adsorbates at reaction conditions. The same behavior was found during the dosage of the single gases CO 2 and CO to these reduced catalysts. The formation of carbonaceous species, detected by Raman spectroscopy, could indirectly hint to the occurrence of carbidation and was especially observed for a good performing catalyst with a medium reduction degree.