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Main Title: Tuning the Rh–FeOx interface in ethanol synthesis through formation phase studies at high pressures of synthesis gas
Author(s): Preikschas, Phil
Plodinec, Milivoj
Bauer, Julia
Kraehnert, Ralph
Naumann d’Alnoncourt, Raoul
Schlögl, Robert
Driess, Matthias
Rosowski, Frank
Type: Article
Abstract: As-prepared materials tested for a catalytic reaction are usually only precatalysts that become active and/or selective under specific conditions. During this initial formation phase, catalysts can undergo a change in their structure, morphology, chemical state, or even composition. This dynamic behavior has a vital impact on reactivity, and we identified that this initial formation phase is also critical for Rh in the catalytic conversion of synthesis gas to oxygenates and ethanol in particular. The syngas-to-ethanol reaction (StE) is a promising alternative route to ethanol from fossil and nonfossil carbon resources. Despite heavy research efforts, rates and selectivities still need to be improved for industrial operations. For this reason, structure–function relationships at industrially relevant reaction conditions must be clarified. Although some in situ and operando studies have been reported, a pressure gap still exists between experimental and process-relevant high-pressure conditions. To overcome this pressure gap and investigate the dynamic behavior of Rh-based catalysts under reaction conditions, we applied a generic method for formation phase studies at high partial pressures of synthesis gas where standard operando methods are inapplicable. Combining integral and local characterization methods before and after a long-term catalytic test of a RhFeOx/SiO2 catalyst (>140 h on stream) allowed us to ascribe a drastic decrease in ethanol formation to a structural change from an unalloyed RhFeOx to an alloyed RhFe/FeOx nanostructure. Our investigation provides an explanation for the great variation of reported catalytic results of RhFe catalysts and their nanostructures in synthesis gas conversion. The structure–function relationship we identified finally provides the opportunity for improved catalyst design strategies: stabilizing the Rh–FeOx interface by preventing RhFe nanoalloy formation. As one example, we report a RhFeOx catalyst on a high surface area Mn2O3 support which decreases the Fe mobility and reducibility through the formation of a (Fe,Mn)Ox mixed surface oxide. Stabilizing the Rh–FeOx interface finally led to stable ethanol selectivity, and the formation of RhFe nanoalloy structures was not observed.
Subject(s): CO hydrogenation
synthesis gas
Issue Date: 17-Mar-2021
Date Available: 4-Aug-2022
Language Code: en
DDC Class: 540 Chemie und zugeordnete Wissenschaften
Sponsor/Funder: DFG, 390540038, EXC 2008: Unifying Systems in Catalysis "UniSysCat"
Journal Title: ACS Catalysis
Publisher: American Chemical Society
Volume: 11
Issue: 7
Publisher DOI: 10.1021/acscatal.0c05365
Page Start: 4047
Page End: 4060
EISSN: 2155-5435
TU Affiliation(s): Fak. 2 Mathematik und Naturwissenschaften » Inst. Chemie
Appears in Collections:Technische Universität Berlin » Publications

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