Single Site Catalysis for Direct Conversion of Methane to Ethylene and Aromatics: Design, Test and Operando Characterization
Physical Chemistry of Solids and Surfaces, Material Characterisation
Final Report Abstract
Olefins such as ethylene and propylene or benzene derivatives are important intermediates for a range of consumer goods such as cosmetics, lubricants, detergents or polymers. The direct and thus cost-saving conversion of methane to these chemicals remains one of the major challenges in chemistry, as the methane molecule is very stable and therefore difficult to activate. Fe and Pt based catalyst with single metal centers ('single site catalyst') embedded in SiO2 or CeO2 matrix were found promising for the direct and effective conversion of methane to ethylene and aromatics. The identification of the active site structure and the understanding of the structural requirements of the Fe©SiO2 and Pt/CeO2 catalyst and the reaction mechanism for the direct methane conversion to gain insight into the mode of action of this new catalyst were the aims of this project. Nowadays, novel catalysts can be made via various routes including the relatively new flame spray pyrolysis method, which allows the production of nano-crystalline materials in one step. This synthesis method was compared to the one widely used method, the wet impregnation. In this project the structure of catalysts was characterized in detail using complementary methods such as electron microscopy, Raman and infrared spectroscopies. The catalytic activity was investigated in detail, including kinetic and deactivation studies. Promising catalyst systems were studied in- situ at high temperature using synchrotron-based X-ray methods such as X-ray absorption spectroscopy In particular, X-ray spectroscopic operando methods were used to study the structure under the demanding reaction conditions at up to 1250 K. The performed study provides an important step forward in understanding the role and evolution of the active sites as well as the underlying product formation pathway. These findings open up new ways to optimize industrially relevant parameters such as reaction temperature and catalyst loading. The key ones can be summarized as following: I. The catalytic activity in MTOH reaction is independent from the preparation method of Pt/CeO2 and the carbonization of the catalysts can be ruled by the space velocity of the feed. II. Merely single-atom Pt sites, but rather Pt nanoparticles encapsulated or directly connected to the reduced ceria support are key for a high performance during the direct nonoxidative conversion of methane. III. Highly dispersed Fe sites resistant to sintering and agglomeration during reaction can be prepared on silica without the need of high-temperature fusing and exhibited a high catalytic performance. This increases the attraction for large scale production of these catalysts due to a simplified preparation route. The significate quality of the X-ray absorption data obtained during these studies combined with the broad temperature window covered by novel microreactor cell are essential parameters for understanding the functionality and also the deactivation behavior of high temperature catalytic reactions, which were hardly accessible with present operando cell designs. Hence, the application of the cell might pave new possibilities for understanding the structure and mechanism of further catalysts during high temperature reactions like oxidative coupling of methane, dry and steam reforming, aromatization and emission control. Moreover, the special design of the operando microreactor permits the combination of complementary characterization techniques such as X-ray diffraction and Raman spectroscopy, further extending its applicability. Different synthesis routes for both Fe and Pt based catalysts with low metal loading led to the formation of single sites in different rates. The metal-support interaction seems to play a significant role for the FSP synthesis. The active role of Ce in MTOH process is revealed.
Publications
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Enhanced methane conversion to olefins and aromatics by H-donor molecules under non-oxidative condition, ACS Catal. 9 (10), 9045–9050 (2019)
J. Hao, P. Schwach, G. Fang, X. Guo, H. Zhang, H. Shen, X. Huang, D. Eggart, X. Pan, X. Bao
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CATACT: The Catalysis Actinide Beamline at KIT, BIKE Workshop 4: Catalyst characterization and operando spectroscopy, Karlsruhe, Germany, 2021
A. Zimina, D. Doronkin, D. Eggart, J.-D. Grunwaldt
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CO2 Reduction over Mo2C-Based Catalysts, ACS Catal. 11 (3), 1624-1639 (2021)
W. Marquart, S. Raseale, G. Prieto, A. Zimina, B. B. Sarma, J.-D. Grunwaldt, M. Claeys, N. Fischer
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Platinum doped ceria catalysts for direct conversion of methane, 54th Meeting of the German Catalysis Society, Weimar, Germany, 2021
D. Eggart, X. Huang, A. Zimina, X. Pan, J.-D. Grunwaldt
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Versatile and high temperature spectroscopic cell for operando fluorescence and transmission x-ray absorption spectroscopic studies of heterogeneous catalysts, Rev. Sci. Instrum. 92 (2), 023106 (2021)
D. Eggart, A. Zimina, G. Cavusoglu, M. Casapu, D. E. Doronkin, K. A. Lomachenko, J.-D. Grunwaldt
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Operando XAS study of Pt doped CeO2 for nonoxidative conversion of methane. ACS Catalysis, 12, 3897–3908. (2022)
D. Eggart, X. Huang, A. Zimina, J. Yang, Y. Pan, X. Pan, J.-D. Grunwaldt
