Instabilities in fixed bed reactors with downwards directed flow for the oligomerization of 1-butene

In this work instabilities in fixed bed reactors with downwards directed flows for the oligomerization of 1-butene were investigated. For very long residence times or very low velocities in combination with strong exothermic reactions, the buoyancy force can exceed the inertia force and the downwards directed liquid flow in the fixed bed becomes instable. These flow conditions might result in hotspots, the shift of the conversion towards unwanted by-products or even in a runaway of the reactor. Therefore, the detailed understanding of the transition between stable and instable flow conditions in fixed bed reactors is essential for a safe and reliable operation of the reactor. Various simulation methods and correlations were applied to predict instable conditions that were observed in an experimental setup. 3D CFD simulations could be used to predict instable flow conditions in fixed bed reactors

Utilizing confined space to attain high performance catalysts and support materials

Der wachsende Energiebedarf und die Abhängigkeit von fossilen Brennstoffen, befeuert die Suche nach erneuerbaren Technologien. Eine mögliche Alternative bietet die PEM Brennstoffzelle. Für eine erfolgreiche Kommerzialisierung sind allerdings noch Weiterentwicklungen insbesondere in der Aktivität und Stabilität des Katalysatormaterials von Nöten. Durch die Applikation von graphitischen Hohlkugeln (HGS) kann, dank der Unterdrückung von Degradationsmechanismen wie Agglomeration, insbesondere die Stabilität signifikant erhöht werden. HGS wurden mit Pt-Co Nanopartikeln und Pt-Ni Nanooktaedern beladen. Darüber hinaus wurden alternative Synthesewege für mesoporöse Katalysatorsupports erschlossen, z.B. mittels chemischer Gasphasenabscheidung von Ferrocen oder der simultanen Polykondensation von Resorcin/Formaldehyd und Kieselsäureestern

The Impact of Antimony on the Performance of Antimony Doped Tin Oxide Supported Platinum for the Oxygen Reduction Reaction

Daniel Jalalpoor, Daniel Göhl, Paul Paciok, Marc Heggen, Johannes Knossalla, Ivan Radev, Volker Peinecke, Claudia Weidenthaler, Karl J. J. Mayrhofer, “The Impact of Antimony on the Performance of Antimony Doped Tin Oxide Supported Platinum for the Oxygen Reduction Reaction”, J. Electrochem. Soc. 168, (2021) 024502 https://doi.org/10.1149/1945-7111/abd830 Abstract:Antimony doped tin oxide (ATO) supported platinum nanoparticles are considered a more stable replacement for conventional carbon supported platinum materials for the oxygen reduction reaction. However, the interplay of antimony, tin and platinum and its impact on the catalytic activity and durability has only received minor attention. This is partly due to difficulties in the preparation of morphology- and surface-area-controlled antimony-doped tin oxide materials. The presented study sheds light onto catalyst–support interaction on a fundamental level, specifically between platinum as a catalyst and ATO as a support material. By using a previously described hard-templating method, a series of morphology controlled ATO support materials for platinum nanoparticles with different antimony doping concentrations were prepared. Compositional and morphological changes before and during accelerated stress tests are monitored, and underlying principles of deactivation, dissolution and catalytic performance are elaborated. We demonstrate that mobilized antimony species and strong metal support interactions lead to Pt/Sb alloy formation as well as partially blocking of active sites. This has adverse consequences on the accessible platinum surface area, and affects negatively the catalytic performance of platinum. Operando time-resolved dissolution experiments uncover the potential boundary conditions at which antimony dissolution can be effectively suppressed and how platinum influences the dissolution behavior of the support

Shape-Controlled Nanoparticles in Pore-Confined Space

Increasing the catalyst’s stability and activity are one of the main quests in catalysis. Tailoring crystal surfaces to a specific reaction has demonstrated to be a very effective way in increasing the catalyst’s specific activity. Shape controlled nanoparticles with specific crystal facets are usually grown kinetically and are highly susceptible to morphological changes during the reaction due to agglomeration, metal dissolution, or Ostwald ripening. A strong interaction of the catalytic material to the support is thus crucial for successful stabilization. Taken both points into account, a general catalyst design is proposed, combining the enhanced activity of shape-controlled nanoparticles with a pore-confinement approach for high stability. Hollow graphitic spheres with narrow and uniform bimodal mesopores serve as model system and were used as support material. As catalyst, different kinds of particles, such as pure platinum (Pt), platinum/nickel (Pt3Ni) and Pt3Ni doped with molybdenum (Pt3Ni–Mo), have exemplarily been synthesized. The advantages, limits and challenges of the proposed concept are discussed and elaborated by means of time-resolved, in and ex situ measurements. It will be shown that during catalysis, the potential boundaries are crucial especially for the proposed catalyst design, resulting in either retention of the initial activity or drastic loss in shape, size and elemental composition. The synthesis and catalyst design can be adapted to a wide range of catalytic reactions where stabilization of shape-controlled particles is a focus