Unifying Concepts in Catalysis (UniCat)
Jules Verne was perhaps the first to have the vision. In his novel 'The Mysterious Island', published in 1874, the science fiction writer wrote: "Yes, my friends, I believe that water will one day be employed as fuel, that hydrogen and oxygen which constitute it, used singly or together, will furnish an inexhaustible source of heat and light. ..." In the 21st century, science has already outgrown this 'fiction'. The idea of producing hydrogen out of water and light is already being practised in reality.
Video: Catalysis for the future
The basic research on this is being conducted, among other places, at Humboldt-Universität's Institutes of Biology and Chemistry in the context of a Cluster of Excellence called 'Unifying Concepts in Catalysis' (UniCat). More than 50 working groups from the fields of chemistry, physics, biology and engineering are working on the research and development of catalysts at UniCat, which is hosted by the Technische Universität Berlin.
On hearing the word catalyst, most of us probably first think of catalytic converters in cars, but catalysts are, in fact, far more common in the world around us than we think. "More than 80 percent of all the chemical products that form the basis of such everyday products as plastics, cosmetics, clothing or drugs need a catalyst during at least one step in their manufacture," explains Christian Limberg, Professor of Inorganic Chemistry at Humboldt-Universität.
But what are catalysts? They are sometimes affectionately dubbed 'marriage brokers'. If you want two molecules to react with each other, this is often only possible with the help of a third substance, a catalyst, which speeds up the reaction and enables it to take place under milder conditions. The catalyst is not used up during the reaction. Adding catalysts can not only cut the cost of certain processes; it can also make it possible to produce more valuable substances. Catalysis is a process that occurs in nature, e.g. in photosynthesis or breathing. "In fact, it's virtually impossible to improve on the efficiency, effectiveness and selectivity of these natural catalysts, or enzymes," says Prof. Limberg. The scientists are therefore taking nature as a model – learning from it or working with natural catalysts.
Certain enzymes – known as hydrogenases – and photosynthesis play an important role in scientists' efforts to produce hydrogen from light and water. During photosynthesis, sugar and oxygen are produced from carbon dioxide and water with the aid of sunlight. Two 'molecular machines' are involved in this process, photosystems I and II. Photosystem II splits water into oxygen, protons and electrons. ¬Hydrogenases are able to produce hydrogen out of protons and electrons.
"In our experiments we directly couple the photosynthesis apparatus of a cyanobacterium with hydrogenases," explains microbiologist Dr. Oliver Lenz, who, together with Bärbel Friedrich, Professor at HU's Institute of Biology, is analysing how bacteria use and produce hydrogen. An oxygen-tolerant hydrogenase is connected with the photosystem in a test tube using genetic-engineering methods. The hydrogenase-photosystem complex produces hydrogen from protons and electrons using light energy. Although hydrogenases are already naturally present in cyanobacteria, they are sensitive to oxygen and therefore unsuitable for direct coupling with photosynthesis, which releases oxygen. This is why oxygen-resistant hydrogenases are used for this purpose. "The production of hydrogen by coupling the hydrogenase and the photosystem represents a milestone on the road to the biological production of hydrogen from light and water."
The next step for the biologists will be to use the hydrogen obtained in this environment-friendly way to produce electricity with a biological fuel cell. The main advantage of the biological fuel cell is that the very expensive and scarce platinum catalyst is not needed.
However, the attempts at hydrogen production are still in their early stages. More basic research is required. For example, the scientists don't yet know exactly why certain hydrogenases are oxygen-resistant. This is one of the questions that the biologists want to solve with the help of UniCat chemists and physicists – for example Christian Limberg's working group, who want to use chemical methods to replicate the catalytic core of the hydrogenase in a model. This is causing the chemists some difficulties, since the active centres of hydrogenases are complex units which are generated in biological systems in a fascinating way using proteins, as though on a workbench. Prof. Limberg hopes they will succeed not only in replicating the enzyme centre, but also in simulating the hydrogenases' operations in a model. The physicists' expertise is helpful here, since they can use spectroscopic methods to find out more about the enzymes' structure.
In addition to the hydrogenases, the chemical modelling studies also focus on oxygenases. Oxygenases can use oxygen to oxidize hydrocarbons into more valuable substances. Another research group in the Cluster headed by theoretical chemist Professor Joachim Sauer is also studying these important reactions. These scientists are looking for suitable heterogeneous catalysts – i.e. purely inorganic solids which facilitate reactions on their surface. "It would be fantastic if we could develop a catalyst that can convert methane into methanol," says Prof. Limberg. As component of natural gas, methane is primarily burned at present, so it has to be transported from the place of occurrence to the consumer. This is difficult to do safely and economically. "Like methane and hydrogen, methanol can also be used as an energy source. However, it has the advantage of being a liquid, making it easier to handle." Only time will tell whether the dream will come true. But there is one thing that the UniCat researchers already know now, and that is that each of them, by contributing their respective specialized methods, is helping to solve problems faster by working together.
- Technische Universität Berlin
- Humboldt-Universität zu Berlin
- Freie Universität Berlin
- Universität Potsdam
- Fritz Haber Institute of the Max Planck Society (FHI)
- Max Planck Institute of Colloids
- and Interfaces in Golm (MPI-KG)