Time- and lateral-resolved X-ray Absorption Fine Structure spectroscopy in a single-shot - A new concept for characterizing catalyst materials at work

• Applicants: Ana Guilherme Buzanich, Ph.D.; Dr. Sebastian Wohlrab
• Subject Area: Analytical Chemistry
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 351914377

This project addresses to the in situ/operando investigation of supported VOx catalysts. Together with the new insights about these materials, the newly developed set-up that combines time- and spatial-resolved XAFS measurements simultaneously at the BAM group will be used. This promotes the present application to novelty. Attractive features of this set-up are: a) probing a larger portion of the sample, especially important for chemically heterogeneous materials, discerning different oxidation states simultaneously; b) scanningless and c) time resolution in the second scale. Given the focus of the present project, varying the support materials by heteroatom doping should result in different redox activities of the active VOx sites. Hence, the key parameters to investigate are local and time dependent changes in oxidation state and coordination geometry of V-species. Depending on the results, the influence on the catalyst performance will be investigated and will be considered for further developments on the catalysts and the reactor set-up. The case study of supported VOx catalysts is very appealing as an alternative for the direct production of formaldehyde from methane. The species planned to be used/tested in this project (mesoporous silica materials) are especially well suited for the desired structural properties of VOx. The measurements will be carried out in a reaction cell with a product analysis at the exit, in order to evaluate the structural changes of the catalyst to correlate directly with the catalytic parameters (operando approach). In the project the experiences at BAM with synchrotron techniques and at LIKAT in catalytic research ideally complement each other. Nowadays, time- and lateral-resolved XAFS experiments exist separately. Facilities offering a combination of both have not yet been reported, to the best of our knowledge. Especially in the field of catalysis, such experiment opens up new opportunities in the combined development of catalysts with a suitable reactor design, e.g. single-bed vs. multi-bed. This integrated experimental approach allows new insight into some challenging problems, e.g. hot spot formation as well as structural dynamics of catalytic active sites. This can help to find new solutions for underlying problems. A suitable reaction for testing such approach is the partial oxidation of methane to formaldehyde which is of great interest in both academia and industry. Moreover, the approach could be used for the structural investigation of catalysts used for other challenging catalytic reactions with methane, e.g. total oxidation, oxidative and nonoxidative coupling, direct methanol production etc. or even for the bunch of unsolved structural questions in catalysis.

• DFG Programme: Research Grants
• Major Instrumentation: FTIR-Spektrometer
• Instrumentation Group: 1830 Fourier-Transform-IR-Spektrometer