@article{JungePuringPiontekSmialkowskietal.2017, author = {Junge Puring, Kai and Piontek, Stefan and Smialkowski, Mathias and Burfeind, Jens and Kaluza, Stefan and Doetsch, Christian and Apfel, Ulf-Peter}, title = {Simple Methods for the Preparation of Non-noble Metal Bulk-electrodes for Electrocatalytic Applications}, series = {Journal of visualized experiments : JoVE}, journal = {Journal of visualized experiments : JoVE}, number = {124}, publisher = {JoVE}, issn = {1940-087X}, doi = {10.3791/56087}, year = {2017}, abstract = {The rock material pentlandite with the composition Fe4.5Ni4.5S8 was synthesized via high temperature synthesis from the elements. The structure and composition of the material was characterized via powder X-ray diffraction (PXRD), M{\"o}ssbauer spectroscopy (MB), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and energy dispersive X-ray spectroscopy (EDX). Two preparation methods of pentlandite bulk electrodes are presented. In the first approach a piece of synthetic pentlandite rock is directly contacted via a wire ferrule. The second approach utilizes pentlandite pellets, pressed from finely ground powder, which is immobilized in a Teflon casing. Both electrodes, whilst being prepared by an additive-free method, reveal high durability during electrocatalytic conversions in comparison to common drop-coating methods. We herein showcase the striking performance of such electrodes to accomplish the hydrogen evolution reaction (HER) and present a standardized method to evaluate the electrocatalytic performance by electrochemical and gas chromatographic methods. Furthermore, we report stability tests via potentiostatic methods at an overpotential of 0.6 V to explore the material limitations of the electrodes during electrolysis under industrial relevant conditions.}, language = {en} } @article{WinterDiehlTelaaretal.2024, author = {Winter, Franziska Luise and Diehl, Patrick and Telaar, Pascal and Watermann, Clara Maria and Kaluza, Stefan and Muhler, Martin and Apfel, Ulf-Peter and Zeidler-Fandrich, Barbara}, title = {Influence of the catalyst precursor for cobalt on activated carbon applied in ammonia decomposition}, series = {Catalysis Today}, volume = {429}, journal = {Catalysis Today}, publisher = {Elsevier}, issn = {0920-5861}, doi = {10.1016/j.cattod.2023.114502}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:due62-opus-46600}, pages = {9}, year = {2024}, abstract = {Ammonia is a key compound for storing and transporting green hydrogen. However, the efficient release of stored hydrogen through thermocatalytic ammonia decomposition is achievable only at temperatures around 600 °C, particularly with non-noble metal-based catalysts, which prove to be both ecologically and economically more feasible. In this study, electrically conductive activated carbon was selected as the catalyst support, chosen specifically for its suitability in achieving more energy-efficient direct reactor heating through the ohmic resistance of the catalysts. Cobalt salts were wet impregnated on activated carbon investigating the influence of different precursors (cobalt nitrate and cobalt acetate) and pyrolysis temperatures (400 °C and 600 °C) under N2 flow on the cobalt particle size and the incorporation of cobalt into the carbon matrix. TEM imaging and CO-chemisorption revealed well dispersed cobalt particles with sizes below 10 nm for the catalysts synthesized from the cobalt nitrate precursor. On the other hand, cobalt acetate led to about nine times larger Co agglomerates, which were partially detached from the carbon matrix. Moreover, this substantial difference in the Co particle size results in a significantly higher ammonia conversion for cobalt nitrate-based catalysts, achieving 94 \% of ammonia conversion at 600 °C. Furthermore, the long-term stability test of the cobalt nitrate-based catalyst resulted in a slight deactivation of only 2 \% ammonia conversion at 500 °C.}, subject = {Katalyse}, language = {en} } @article{GreuelWatermannLohmannetal.2025, author = {Greuel, Marc and Watermann, Clara Maria and Lohmann, Heiko and Kaluza, Stefan and Apfel, Ulf-Peter and Zeidler-Fandrich, Barbara}, title = {The conversion of ethanol over 3d-metal saponite-like smectites}, series = {Materials Advances}, journal = {Materials Advances}, number = {6}, publisher = {Royal Society of Chemistry}, issn = {2633-5409}, doi = {10.1039/d4ma01036a}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:due62-opus-52973}, pages = {2885 -- 2898}, year = {2025}, abstract = {The replacement of fossil fuel processes with renewable pathways is critical to circumvent climate change and environmental risks. A process of interest is the production of 1,3-butadiene (BD), which is primarily derived as a by-product of naphtha steam cracking. A sustainable alternative path involves converting renewable ethanol to BD via the Lebedev process, which requires a catalyst with balanced redox, acidic, and basic sites. Due to the necessity of a multifunctional catalyst, existing materials for this reaction are either comprised of catalyst mixtures or supported catalysts. In this study, we introduce a bulk material, saponite, containing M-O-Si sites, which combine required catalytic sites for the ethanol to BD (ETB) reaction in one material. The product composition in ethanol conversion were strongly dependent on the type of 3d-metal used, while no conclusive correlation between surface properties, conversion, and product composition was observed. Herein, using V-Sap*, we achieved an ethene productivity of 448 gethene kgcat-1 h-1 (74\%) at 573.15 K. High acetaldehyde productivity was maintained with Cu-Sap* (466 gAcA kgcat-1 h-1, 49\%) at 573.15 K and Zn-Sap (528 gAcA kgcat-1 h-1, 55\%) at 723.15 K. Mg-Sap primarily produced ethene but also yielded 10 gBD kgcat-1 h-1 BD at 723.15 K. Higher BD outputs were observed with Ni-Sap (31 gBD kgcat-1 h-1 at 523.15 K) and Mn-Sap* (51 gBD kgcat-1 h-1 at 723.15 K). This underscores the potential of saponite-based materials for flexible product outputs in ethanol conversion, influenced by the choice of integrated 3d-metal.}, subject = {Butadien}, language = {en} }