Catalysts without Precious Metals Turning Carbon Dioxide into Useful Chemicals

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Artificial photosynthesis is the topic of a junior research group at the Institute of Chemistry. The researchers want to develop precious metal-free catalyst materials to process carbon dioxide with the help of sunlight.

Harnessing the power of the sun to convert the greenhouse gas carbon dioxide into useful chemicals — that is the goal of a new junior research group at the University of Oldenburg. The international team led by chemist Dr. Lars Mohrhusen is pursuing a particularly sustainable approach: the researchers are planning to develop precious metal-free catalysts that chemically activate the rather inert greenhouse gas with the help of sunlight. The Federal Ministry of Education and Research (BMBF) is funding the Su2ncat-CO₂ project over the next six years with around 2.6 million euros under the Sinatra funding guideline (junior research groups for “Artificial Photosynthesis” and “Use of Alternative Raw Materials for Hydrogen Production”).

“The work of the new junior research group aims to find inexpensive and long-term stable materials to replace precious metal catalysts currently in use. The BMBF's funding approval recognizes the University of Oldenburg's great interdisciplinary expertise in the fields of catalysis and nanomaterials and underlines the great importance of this research for society,” says Prof. Dr. Ralph Bruder, President of the University of Oldenburg.

In his project, Mohrhusen and his group want to develop catalyst materials based on readily available and inexpensive ingredients such as titanium dioxide. The aim is to convert the greenhouse gas carbon dioxide into substances such as methane, methanol or formaldehyde with as little energy input as possible, which can then be further processed by the chemical industry into plastics or synthetic fuels, for example. “Until now, catalysts containing precious metals have usually been used to convert substances such as carbon dioxide, often at high pressure and high temperatures,” explains Mohrhusen. In addition to the large amount of energy required to achieve the right reaction conditions, these materials often have the disadvantage of being expensive and not particularly durable. For example, impurities can easily poison the catalyst material, making it less active over time.

In the project, Mohrhusen and his team want to investigate two different model systems of hybrid catalyst materials. On the one hand, combinations of titanium dioxide with semi-metal nanoparticles are to be produced, and on the other, organic structures on oxide surfaces. The researchers then want to characterize these systems with microscopic precision using different methods, which usually requires ultra-high vacuum conditions. In both cases, these are so-called photocatalysts, i.e. catalysts that become catalytically active when exposed to light: The solar radiation generates charge carriers in the material — negatively charged electrons and positively charged, mobile defects, so-called holes. These can then react chemically with carbon dioxide. “Using these model catalysts, we want to understand in detail at an atomic level which material properties contribute to the reactivity, but also to the stability of the systems,” says Mohrhusen. This is often not easily possible under technical conditions in large reactors.

In a third sub-project, the team wants to develop micro-test reactors in order to test the model catalysts under more realistic conditions. The materials are brought into contact with a gas mixture — consisting of carbon dioxide, hydrogen and water, for example — in a special chamber and simultaneously irradiated with light. Meanwhile, the researchers analyze the formation of the reaction products. They can also investigate any structural changes to the catalyst materials caused by the reaction after the tests have been completed.

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