Metal-free “green” polymer-derived carbon that replaces catalysts and nanocarbons

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Catalysts are an important material in modern society, allowing them to selectively convert raw materials into valuable products while reducing waste and saving energy. For industrially relevant oxidative dehydrogenation reactions, the most well-known catalytic systems are based on transition metals such as iron, vanadium, molybdenum, or silver. Due to the inherent shortcomings associated with the use of transition metals, such as rare occurrences, environmentally harmful mining processes, and toxicity, pure carbon exhibits catalytic activity in this type of reaction, making it a likely sustainable alternative. The fact that it is hidden is of great interest.

To date, the development of carbon-based catalysts for oxidative dehydrogenation can be divided into two generations. First-generation carbon catalysts were inspired by the discovery of the catalytic activity of coke deposits on metal-based catalysts for oxidative dehydrogenation. Subsequently, amorphous carbon materials such as activated carbon and carbon black were mainly investigated. Although these early catalysts showed significant activity and selectivity, they were poorly oxidatively stable and later became second-generation carbon-based dehydrogenation catalysts represented by carbon nanomaterials such as carbon nanotubes. It was taken over. The advantages of nanocarbons over first-generation amorphous catalysts are primarily due to their crystalline microstructure. This involves proper oxidation resistance on the one hand and allows high redox activity on the other. Due to the lack of internal porosity of nanocarbons, these active sites are located on the outer surface, providing easy access to the reactants. However, nanocarbons still await industrial use as catalyst materials as they present drawbacks and unclear health risks during the handling of powders and fixed floors.

Professor Bastian JM Etzold’s research group has taken into account the high potential of carbon catalysts in oxidative dehydrogenation reactions, with the aim of shifting the superior catalytic properties of nanocarbons to conventional simple ones. I have been working on carbon synthesis for several years. Process carbon material. As early as 2015, it was shown in principle that carbon derived from carbides could be used to achieve catalytic properties similar to carbon nanomaterials. However, since carbon derived from carbides is complicated to synthesize, it is only a model material for research purposes, so the basic research goal is to develop a scalable and reproducible synthetic route to technically useful carbon catalysts. Remains. He received his PhD in collaboration with Professor Wei Qi of the Shenyang National Institute of Materials Science in Shenyang, China, and Professor Jan Philipp Phofmann of the Surface Science Institute of TU Darmstadt and Felix Herold. Students in the Etzold group have succeeded in synthesizing a new generation of carbon catalysts that are in many ways superior to nanocarbon.

The synthesis of new carbon catalysts is based on polymeric carbon precursors that can be produced by a reproducible and easily extensible synthetic pathway, while providing excellent control of subsequent carbon morphology. Using catalytic graphitization, it has been demonstrated that nanoscale graphite microcrystals can grow within the carbon matrix during the thermal decomposition of the polymer precursor. The basis in this context appears to be the presence of large conjugated (graphite) domains characterized by high density defect sites where oxygen surface groups such as ketone carbonyl groups are formed during the reaction. The activity of these surface groups appears to increase via adjacent conjugated (graphite) domains and can function as electron stores. Contact graphitization produces an amorphous / graphite hybrid material consisting of pre-grown graphite microcrystals surrounded by an amorphous carbon matrix. To obtain an active dehydrogenation catalyst, the amorphous carbon matrix is ​​removed by selective oxidation, opening the pore structure of the carbon material and providing access to the catalytically active graphite domain.

Oxidative dehydrogenation of ethanol is a very interesting test in practice because it provides a catalytic link between bioethanol, which is readily available from renewable resources, and acetaldehyde, an important intermediate in current industrial chemistry. Selected as a reaction. Compared to the benchmark carbon nanotube catalysts, the new class of carbon materials achieved up to 10 times the space-time yield.

The new carbon catalyst presented in this study is very important as it opens the door to a new class of materials. Due to the possibility of multiple optimizations of flexible synthetic routes, that possibility has not yet been evaluated. In addition to the use of new classes of carbon catalysts in the oxidative dehydrogenation of other related substrates such as alkanes and other alcohols, it is also expected that their scope will be extended to electrocatalysts and photocatalysts.

Carbon-based catalyst used in Fischer-Tropsch synthesis

For more information:
Felix Herold et al, Nanoscale Hybrid Amorphous / Graphite Carbon as Key to Next Generation Carbon-Based Oxidative Dehydrogenation Catalysts, Angewandte Chemie International Edition (2021). DOI: 10.1002 / anie.202014862

Courtesy of Technische Universitat Darmstadt

Quote: Metal-free “green” polymer-derived carbon (February 4, 2021) as a metal-free alternative to catalysts and nanocarbons is available at Obtained from -metal on February 4, 2021. -free-green-alternative.html

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Metal-free “green” polymer-derived carbon that replaces catalysts and nanocarbons

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