Golden Ball Mills as Green Catalysts

A gold-plated grinding vessel for ball mills proved to be a real miracle in a research project in inorganic chemistry at Germany’s Ruhr University: a team led by Professor Lars Borchardt was able to use it without any solvents or environmentally harmful chemicals. Converts alcohols to aldehydes. The catalytic reaction takes place on the gold surface and is mechanically driven. The vessel can be reused many times. „This opens up new opportunities for the use of gold in catalysis and shows how traditional materials can contribute to solving modern environmental problems in an innovative way,” says Borchardt. The team reports in the journal Angewandte Chemie from May 27, 2024.

Aldehydes are essential compounds in the chemical industry and are used in the manufacture of medicines, vitamins and perfumes. Of particular importance is the selective oxidation of alcohols to aldehydes without secondary reactions. Over-oxidation often occurs with many conventional methods, resulting in the formation of unwanted by-products such as carboxylic acid and esters. Traditional alcohol oxidation methods often require the use of solvents and environmentally harmful chemicals. They not only produce harmful waste but also pose significant health risks to users. Additionally, high temperatures and pressures are often applied, which can break temperature-sensitive substrates.

Reusable vessels

Instead the Bochum team uses mechanical chemistry: ball mills, typically used to grind materials, are used to conduct chemical reactions. An important advance has been the use of grinding vessels coated with a thin layer of gold a few nanometers thick. „Because we found that the reaction occurs exclusively on the surface of gold, we were able to limit ourselves to very small amounts of the precious metal by simply coating the grinding vessel,” says lead author Maximilian Wohlkemuth. „The vessels can be reused in many different reactions.”

The catalytic reaction takes place directly in the ball mill, without the use of harmful solvents and under mild conditions, which preserves the integrity of the substrates and increases energy efficiency. „Our method produces significantly less waste and dispenses with the cost-effective production of molecular gold compounds or gold nanoparticles,” summarizes Wohlgemuth. This makes the process not only more sustainable, but also more cost-effective.

Transferable to many areas of chemistry

The introduction of gold as a catalyst in mechanochemical processes has potential applications in many areas of chemistry. „Our results pave the way for further research and developments based on the use of precious metals in environmentally friendly processes,” says Lars Borchardt. „The combination of high efficiency, low environmental impact and cost-effectiveness makes our method a promising approach for the future of chemistry.”