Using catalysts activated by sunlight, researchers in Germany are looking at ways to turn carbon dioxide into substances such as methanol.
A research group at the University of Oldenburg is trying to develop precious-metal-free catalysts that use sunlight to chemically activate CO2.
The international team led by chemist Lars Mohrhusen will focus on developing catalyst materials based on readily available and inexpensive components, such as titanium dioxide. The aim is to find highly energy-efficient ways to convert the greenhouse gas carbon dioxide into compounds such as methanol, formaldehyde or ethylene, which can be used by the chemical industry in the manufacture of plastics or synthetic fuels.
“The conversion of substances like carbon dioxide generally involves precious-metal-containing catalysts, which often require high pressure and high temperatures during operation,” Mohrhusen explains.
In addition to the large amounts of energy required to create the right conditions to trigger a reaction, these materials often have the disadvantage of being expensive and not particularly durable. Impurities in the gas feed, for example, can easily “poison” the catalyst material so that it becomes less active over time, Mohrhusen says.
Mohrhusen's team plans to investigate two different types of hybrid catalyst materials in model systems. For this, they will create combinations of titanium dioxide and semi-metal nanoparticles as the first class of materials, and organic structures on oxide surfaces as the second. In the next step, the researchers will use various techniques to characterize the systems at the atomic level – a process which typically requires ultra-high vacuum conditions.
Both material classes will be photocatalysts, meaning that they become catalytically active when exposed to light. Their exposure to sunlight generates charge carriers – negatively charged electrons and positively charged “vacancies,” so-called “holes” that can then react chemically with carbon dioxide.
“On the basis of these model catalysts we aim to gain a detailed, atomic-level understanding of which material properties enhance the reactivity as well as the stability of these systems," says Mohrhusen.
This can be very difficult under the technical conditions that prevail in large reactors, he explains.
In a third sub-project the team plans to design micro reactors to test the model catalysts under more realistic conditions. This will involve bringing the catalyst materials into a gas atmosphere – a combination of carbon dioxide, hydrogen and water, for example – in a special chamber and simultaneously irradiating them with light. The researchers will analyze the formation of reaction products during the process and can also examine the catalyst materials for structural changes caused by the reaction once the tests have been completed.
