At the Unifying Systems in Catalysis (UniSysCat) Cluster of Excellence at the Technische Universität Berlin, scientists research the future of “green chemistry”. The aim of this is to conserve resources, work in an energy-efficient manner and avoid waste.

Greenopolis looks like something out of modern science fiction: a factory city with trees growing on the roofs which does not produce any waste. Only clean water flows from the beak-shaped drainpipe that feeds into the moat surrounding the city. This is how, in a comic, the Unifying Systems in Catalysis (UniSysCat) Cluster of Excellence at the Technische Universität Berlin is presenting the basic principle of its research: to learn from nature in order to ensure people’s quality of life.

In the short introductory film that the Cluster of Excellence is showing in the Humboldt Lab’s opening exhibition, “According to Nature”, this principle is illustrated using the example of photosynthesis: plants absorb carbon dioxide and water and, with the help of light energy, convert them into oxygen and sugar – substances that other organisms need to live. An ingenious concept that harnesses the natural energy of the sun and does not produce any waste. Plants thus counteract the man-made climate crisis, because they absorb and convert the greenhouse gas carbon dioxide. Plant-based foods are created for animals and humans, and plenty of wood is generated, which is a safe and useful form of storage for solar energy.

The UniSysCat scientists want to understand what happens during these kinds of process in which lots of individual chemical reactions build on one another. “The next step is then about recreating structures like these and watching to see what changes when we turn certain screws,” explains Holger Dobbek, Professor of Structural Biology and Biochemistry at the Humboldt-Universität and one of the spokespersons of the Cluster of Excellence. The aim is to take a leaf out of the book of natural processes like photosynthesis so as to be able to create new compounds using light and, for instance, produce fuel from light using carbon dioxide and water. “What we’re doing is like if we were to reinvent nature all over again,” says cluster spokesperson Arne Thomas, Professor of Functional Materials at the Technische Universität Berlin.

Green chemistry: conserving resources and bringing products into a cycle

Emulating nature is certainly good, but improving on it sounds insanely challenging. And it is. For, the great role model not only runs a huge, worldwide network of photosynthesis factories with its forests; it also has a certain head start. “Plants have built up this apparatus over millions of years,” says cluster spokesperson Matthias Drieß, Professor of Organometallic Chemistry & Inorganic Materials at the Technische Universität Berlin. Humans don’t have that much time, stresses the chemist. “If we wait that long, we will be left with gargantuan, human-generated amounts of the climate-killing gas carbon dioxide, with devastating consequences.” For, due to advancing climate change and the production of plastic and toxic waste products, mankind is working its way towards the slow but sure destruction of the earth.

Plastic and other polymers come from the chemical industry. They pose a huge waste problem – another reason, Matthias Drieß urges, why chemistry has to become greener, but also more ethical; that is, why it must address the effects of chemical products in the environment.

Millions of tonnes of plastic are produced each year without any comprehensive solution for their recycling as urban raw materials. This is where chemistry is needed, emphasises the spokesperson for the Cluster of Excellence: “One has to produce polymers that one knows can be elegantly broken down again into their basic components.” This is how nature does it. It makes something and then breaks it down again into its individual parts – without generating any waste in the process.

The term “green chemistry” stands for sustainability. That means: “Everything comes into being, perishes, and is part of a reliable ecosystem. It fits into one big whole – without any ecologically hazardous waste products,” explains Drieß. Another basic tenet of green chemistry is to conserve resources by using substances that are prevalent, explains Arne Thomas. It is also about using energy as sparingly as possible. It is true that nature itself is sometimes wasteful when it comes to energy consumption, says Holger Dobbek. But that only applies to areas where there is enough of it available. Bacteria, for instance, are an example of the greatest possible energy efficiency. They can get by with an absolute minimum.

Revolutionizing catalysis

At the heart of the processes that are being researched at UniSysCat is catalysis. The Cluster of Excellence has set itself the goal of “revolutionising catalysis”. Sounds impressive, but what does it mean? The film that UniSysCat is showing in the Humboldt Lab explains this using a chemistry lesson classic: the oxyhydrogen reaction. A balloon is filled with a mixture of hydrogen and oxygen. As soon as a flame is brought near, the balloon explodes – water and oxygen react to form water. However, if a catalyst is used, there is no longer any need for a flame. A catalyst is an auxiliary substance that reduces the energy required to set a chemical reaction in motion. It also speeds up the reaction. Catalytic processes form the basis for the production of many everyday items – from detergents to medicines, plastics and adhesives, to mobile phones and computers.

This often results in waste products that are difficult to dispose of. There are reasons, says Dobbek, why chemistry has such a bad reputation. After all, it is not by chance that the term causes many people to think of unpleasant-smelling factories with clouds of smoke rising up from their chimneys into the sky.

In Greenopolis, the imaginary dream city of the UniSysCat scientists, things are different. One example of a new catalytic process that is being established to conserve resources and avoid waste, and which is being researched at the Cluster of Excellence, is the manufacture of vitamin A, which the human body cannot produce itself, says Matthias Drieß. It is needed in huge quantities, above all as a nutritional supplement, and especially in factory farming and in cosmetics. “The scales we are talking about here thus go without saying. If you look at food packaging, vitamin A is often added. This does not come from cod liver oil or carrots, but from the chemical industry, because the demands are very high.”

So far, however, no catalysts have been used in the production process. Thus, waste piles up that needs to be recycled in an energy-intensive manner, explains the chemist. This is why, for the first time, a catalytic cycle process is being developed in which the starting materials are converted without the generation of waste by means of an electric current at the electrodes of an electrolysis cell.

Scientists from the fields of chemistry, biology, physics and engineering conduct research together at UniSysCat. Their aim is to connect complex chemical and biological reactions in modern systems so that one is left at the end with products that can be recycled, for example for medicines or cosmetic products.

The Cluster of Excellence, which builds on its predecessor, the UniCat cluster, started its research projects in the summer of 2019. In addition to scientists from the universities in Berlin and Potsdam, representatives of several research institutes are also involved, including from the Fritz Haber Institute (FHI) of the Max Planck Society and the Helmholtz Centre Berlin (HZB). In 2018, the “John Warner Center for start-ups in Green Chemistry” was founded as a centre to promote innovative ideas in the field of green chemistry. Perhaps, in future, this will be the birthplace of lots of little Greenopolises.