Time- and lateral-resolved X-ray Absorption Fine Structure spectroscopy in a single-shot - A new concept for characterizing catalyst materials at work
Final Report Abstract
This project succeeded on two veins of research: one that aimed at structure clarification of supported catalysts used for direct conversions of methane, and one that focused on in situ/operando investigations of catalysts at work with a new setup for dispersive X-ray absorption spectroscopy (DXAS), with 3D information in one shot, entailing time, space and energy. Our initial case study of supported VOx catalysts is very appealing for producing formaldehyde directly from methane. The highest productivity has so far been achieved for formaldehyde using silica-supported VOx catalysts with over 5 kgCH2O‧kgcat^-1‧h^-1. Building on this, the productivity of these systems was further increased. This was achieved by optimizing the synthesis parameters for V-MCM-41 and V-SBA-15, by transition metal modification of the carrier material and by modelling and optimization with the aid of artificial neural networks. After detailed characterization and understanding the catalysts, new maximum productivity values of over 13 kgCH2O‧kgcat^-1‧h^-1 were achieved for all systems. As to the DXAS setup, the features to be highlighted are: a) sampling of a larger section of a sample, which is especially important for heterogeneously distributed materials, so that different oxidation states can be recorded across the sample; b) no scanning; and c) time, space, and energy resolution in the seconds (s), micrometres (µm), and electron-volts (0.5 eV) scales respectively, in one shot. A vital part of this project was the development of a custom-made reactor, with a product analysis at the output to obtain a direct coupling between structural change and catalytic parameter (operando method). The reactor, adapted for the XAS experimental setup, hosts the catalyst bed allowing it to be submitted to a reaction gas flow mixture of 360.000 ml gcat^-1 h^-1 while heating up to 650 °C. The feasibility of the new experimental setup for dispersive XAS was demonstrated on another well-known, but less understood, catalytic conversion where in situ analysis is of particular interest: the methane dehydroaromatization (MDA) over Mo/HZSM-5 catalysts. Our new method represents an unprecedented addition to the analytical toolbox for in situ characterizations. Especially with respect to catalysis, such experiments are trendsetting with respect to combined catalyst and reactor design (such as from single to multiple catalyst feeds). This project was unfortunately characterized by the following delays, which, however, could be countered with a cost-neutral extension of the project duration: (1) The departure of a Postdoc, which interrupted the rhythm and flow of the project. (2) The damage to the introductory device at BAMline in 2019. (3) The outbreak of the COVID-19 pandemic in early 2020.
Publications
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Combination of Chemo- and Biocatalysis: Conversion of Biomethane to Methanol and Formic Acid. Applied Sciences, 9(14), 2798.
Kunkel, Benny; Seeburg, Dominik; Peppel, Tim; Stier, Matthias & Wohlrab, Sebastian
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Influence of hydrothermal ageing time on the performance of in situ prepared VMCM-41 catalysts in the selective oxidation of methane to formaldehyde. Microporous and Mesoporous Materials, 288, 109581.
Seeburg, Dominik; Bentrup, Ursula; Kunkel, Benny; Ha, Vu Thi Thu; Dang, Thi Thuy Hanh & Wohlrab, Sebastian
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Increasing the Efficiency of Optimized V-SBA-15 Catalysts in the Selective Oxidation of Methane to Formaldehyde by Artificial Neural Network Modelling. Catalysts, 10(12), 1411.
Kunkel, Benny; Kabelitz, Anke; Buzanich, Ana Guilherme & Wohlrab, Sebastian
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Enhancement and limits of the selective oxidation of methane to formaldehyde over V-SBA-15: Influence of water cofeed and product decomposition. Catalysis Communications, 155, 106317.
Kunkel, Benny & Wohlrab, Sebastian
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Dispersive x-ray absorption spectroscopy for time-resolved in situ monitoring of mechanochemical reactions. The Journal of Chemical Physics, 157(21).
Guilherme, Buzanich Ana; Cakir, C. Tufan; Radtke, Martin; Haider, M. Bilal; Emmerling, Franziska; F., M. de Oliveira Paulo & Michalchuk, Adam A. L.
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Time-, space- and energy-resolved in situ characterization of catalysts by X-ray absorption spectroscopy. Chemical Communications, 59(81), 12120-12123.
Peters, Stefan; Kunkel, Benny; Cakir, Cafer Tufan; Kabelitz, Anke; Witte, Steffen; Bernstein, Thomas; Bartling, Stephan; Radtke, Martin; Emmerling, Franziska; Abdel-Mageed, Ali Mohamed; Wohlrab, Sebastian & Guilherme, Buzanich Ana
