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Πέμπτη 21 Ιουνίου 2018 στις 12 το μεσημέρι
στην αίθουσα Γενικών Συνελεύσεων του κτηρίου Δ (ισόγειο) με θέμα:
Modified Ferrites as Catalysts
for High Temperature Water Gas Shift Reaction for Membrane reactors
Ομιλητής: Panagiotis G. Smirniotis
Department of Chemical & Environmental Engineering, University of Cincinnati, USA
Nowadays hydrogen is considered to be the most important candidate for a clean energy carrier. As it can be produced from renewable energy sources, it represents one possibility to reduce the negative impact of civilization on the environment such as the greenhouse effect and air pollution. Most of the processes require high purity hydrogen. Production of hydrogen using membrane reactors via high temperature water gas shift reaction has received much importance in recent years because hydrogen can be selectively permeate through a membrane, and produce high purity hydrogen. The WGS reaction in a membrane reactor (MR) is potentially capable of completing the CO conversion and achieving simultaneous H2/CO2 separation in a single stage operation. A membrane for this reaction typically operates at 450 oC to 550 oC temperatures and pressures ranging from 1-25 bars. Development of catalysts for membrane reactors operating at these high pressures and temperatures have to meet stringent requirements.
The present study is aimed at developing various modified ferrite catalysts for high temperature WGS membrane reactor applications. The idea was to stimulate the ferrite formation via doping with certain foreign cations and to stabilize the Fe3+ <=> Fe2+ redox couple. For this purpose, various doped modified ferrite catalysts were prepared using industrially economical and environmental friendly ammonia assisted coprecipitation method. The WGS reaction carried out in the temperature region 400-550 oC and at a stream to CO ratio 3.5 and 1.5 which the conditions used in our membrane reactor. Temperature programmed reduction measurements (TPR) inferred that Cu selectively promotes the reduction of Hematite (Fe2O3) to Magnetite (Fe3O4) in all modified ferrite catalysts. However, Cu does not promote the reduction of Magnetite to Wustite or reduction of other-metal oxide present in the ferrite. Mössbauer effect studies show distortions in the Fe local environments when Cu is co-doped in Magnetite. These distortions are reflected in the internal magnetic field at octahedral sites with characteristic isomer shift ‘d’. Mössbauer effect results also show that Cu enters at M- modified octahedral sites in Magnetite upon activation of the catalysts to replace Fe2+ ions at octahedral sites, and in general, promotes the WGS activity. The Mössbauer spectra and XPS measurements show that Cu plays different role on Fe3+/Fe2+ redox chemistry in the bulk and surface. During the activation some of the Cu enters at the octahedral sites of the Magnetite and replaces Fe2+ ions and remaining Cu forms metallic Cu species except for the Fe/Ce. Our studies on environmental friendly catalysts and their application in membrane reactors will be discussed will be presented.