Reading the shadows

A team from the Inorganic Chemistry department has developed a mini reactor that enables them to observe chemical reactions "live". The reactor assembly will soon be available to researchers all over the world at DESY (Deutsches Elektronen-Synchrotron).

Man with laboratory equipment
© Julia Siekmann

Niclas Heidenreich was involved in developing the approximately 20cm tall container, inside which he investigates unusual framework compounds consisting of metal atoms and organic molecules, amongst other things.

However, the project is not without its risks, even though this particular reactor has nothing at all to do with atomic energy. The name of the approximately 20cm tall container is based on the chemical react­ions that occur inside it under precisely definable conditions.

Using it requires a screened room with thick iron doors; after all, the scientists inside are working with X-rays. They are basically the same as the ones used in medical examinations of the human body. "But the radiation we use is very much more intense, at least a million times so," explains chemist Niclas Heidenreich, who coordinated the development of the reactor. The container is being set up at the DESY research centre as part of PETRA III. This places the world's most brilliant storage-ring-based X-ray radiation source in Northern Germany.

The 29-year-old doctoral researcher is completing his thesis on the development of the reactor under Professor Norbert Stock at the Institute of Inorganic Chemistry. Stock and his working group are particularly interested in MOFs (metal-organic frameworks), special framework compounds consisting of metal atoms and organic molecules that form cavities of up to five nanometres. "This results in extremely microporous materials similar to zeolites. They are able to take up guest molecules through their pores that interact with the surrounding walls," Stock highlights their special feature. Zeolites are used, for instance, in crude oil refining, in the catalytic converters of diesel engines, and as water softeners in detergents.

"MOFs have several regulating screws that can be used to change their construction and their interaction with guest molecules. That is why it is so interesting for us to target these compounds as specifically as possible," explains Heidenreich. In practice, however, the project was not without its challenges. "As a general rule, we usually only know the starting conditions of chemical reactions and their outcome, the product. But we do not know what is happening while this is going on," continues the chemist. Several factors may influence the synthesis of MOFs, such as the reaction temperature or the resulting pressure.

The new reactor enables the scientists to observe the formation of these porous materials, and the interchange between the molecules and the pore walls, in real time and with precision. But this is not to say that they can watch the chemical sequences through a window in the reactor. Instead, they bombard it with the intensive X-rays and then read the resulting data from the computer. "What we see is effectively a shadow that enables us to draw conclusions regarding what has just happened," explains Heidenreich.

It took almost three years to develop the reactor, and it required a number of prototypes by the institute's workshop and numerous tests at DESY. The measuring facilities in Hamburg run day and night, and researchers all over the world are applying for the highly-coveted utilisation periods.

"The proximity to DESY is a terrific locational advantage for us. It means our doctoral researches and students are also able to attend the utilisation times," explains Stock. He and his team consciously designed the reactor to be flexible in order to cover the greatest possible bandwidth of experiments. Heidenreich is currently writing a user manual to make working with the reactor easier for other researchers. The construction is due to be completely finished in spring, his doctoral thesis a short time later. They made four of them at the same time in order to equip the new particle accelerator MAX LAB IV in Lund in Sweden as well as DESY.

Author: Julia Siekmann