Spatially‐Resolved Insights Into Local Activity and Structure of Ni‐Based CO2 Methanation Catalysts in Fixed‐Bed Reactors

On a Ni/Al2O3 and a Ni−Fe/Al2O3 catalyst spatial concentration and temperature profiles were determined that occur along the axial direction of the catalyst bed. They were correlated to structural gradients under reaction conditions to elucidate the local dependency of catalyst structure on reaction...

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Bibliographic Details
Published in:	ChemCatChem 2021-07, Vol.13 (13), p.3010-3020
Main Authors:	Serrer, Marc‐André, Stehle, Matthias, Schulte, Mariam L., Besser, Heino, Pfleging, Wilhelm, Saraҫi, Erisa, Grunwaldt, Jan‐Dierk
Format:	Article
Language:	eng
Subjects:	Aluminum oxide Carbon dioxide Carbon dioxide hydrogenation Catalysts Concentration and Temperature Profiles Fourier transforms Infrared spectroscopy Iron Methanation Nickel Nickel-Iron Methanation Catalyst Oxidation Reactors Spatially-resolved operando study Spectrum analysis Temperature profiles Valence Vapor phases
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Summary:	On a Ni/Al2O3 and a Ni−Fe/Al2O3 catalyst spatial concentration and temperature profiles were determined that occur along the axial direction of the catalyst bed. They were correlated to structural gradients under reaction conditions to elucidate the local dependency of catalyst structure on reaction‐induced changes of the gas phase. The quantitative concentration and temperature profiles revealed a hotspot in the first third part of the fixed‐bed, which led to by‐product formation of CO. Complementary structural information obtained by spatially‐resolved quick X‐ray absorption spectroscopy unraveled a strong impact of reaction‐induced gradients in gas phase on the oxidation state of Fe with a higher oxidation state towards the end of the catalyst bed, while Ni was only slightly affected. Diffuse reflectance infrared Fourier transform spectroscopy further revealed that addition of Fe to a Ni/Al2O3 catalyst reduces the amount of adsorbed CO species. Hence, Fe hampers blocking of active Ni0 sites by CO and preserves a high fraction of reduced Ni species. Furthermore, an alternative reaction pathway observed on Ni−Fe provided locally a higher activity for CO2 hydrogenation. Overall, the importance of considering local gradients in catalytic reactors is demonstrated. Operando study: Ni and Ni−Fe based catalysts are investigated during CO2 methanation in a spatially‐resolved manner using two fixed‐bed reactor setups to resolve gradients along the catalyst bed. By combining the results of local activity/temperature measurements with spatially‐resolved characterization via quick X‐ray absorption spectroscopy, the local catalyst structure is derived in axial direction and correlated to reaction‐induced changes in gas phase.
ISSN:	1867-3880 1867-3899