Demystifying Science: X-Rays Unravel the Process of One of Nature’s Most Robust Bonds Being Broken

In a groundbreaking study, scientists have elucidated how an activated catalyst can dismantle robust carbon-hydrogen (C-H) bonds in alkanes like methane, a potent greenhouse gas. This reveals that a quick burst of light is enough to activate the catalyst, which then proceeds to break the C-H bonds with minimal energy. The researchers, utilizing powerful X-ray light sources, SwissFEL and Swiss Light Source, traced the process from inception to completion, observing the intricate electron exchange between the catalyst and the C-H group. Advanced quantum-chemical calculations were instrumental in interpreting this complex process, paving the way for more effective catalysts in the chemical industry. These could transform harmful methane and other alkanes into beneficial chemicals.

According to a report published in Science, scientists have successfully decoded how an activated catalyst dismantles the robust carbon-hydrogen bonds in the powerful greenhouse gas, methane. Utilizing advanced X-ray technology and quantum-chemical calculations, they followed the electron exchange between the catalyst and the methane molecule. This progress could lead to the development of more effective catalysts capable of converting detrimental gases into beneficial chemicals.

Scientists are now one step closer to developing more effective catalysts for converting the greenhouse gas methane into a less harmful chemical. This is due to their ability to use quick bursts of X-ray light, a significant development in the field. This groundbreaking result, published in the journal Science, uncovers for the first time how the carbon-hydrogen bonds in alkanes break and how the catalyst aids in this reaction.

Methane, a highly potent greenhouse gas, is increasingly being released into the atmosphere due to livestock farming and the continued thawing of permafrost. If we could convert methane and other long-chain alkanes into less harmful and indeed beneficial chemicals, this would eliminate associated threats and provide an enormous resource for the chemical industry. However, the first step in transforming methane requires breaking a C-H bond, one of nature’s most robust chemical connections.

Four decades ago, it was discovered that molecular metal catalysts could easily split C-H bonds. The only prerequisite was a brief burst of visible light to “activate” the catalyst, and the robust C-H bonds of alkanes could then be easily broken, virtually without any energy use. Despite the importance of this C-H activation reaction, the operation of the catalyst remained a mystery over the years.

The research was headed by scientists from Uppsala University, in collaboration with the Paul Scherrer Institute in Switzerland, Stockholm University, Hamburg University, and the European XFEL in Germany. For the first time, these scientists were able to directly observe the catalyst in action and reveal how it breaks the C-H bonds.

In two experiments conducted at the Paul Scherrer Institute in Switzerland, the scientists tracked the delicate electron exchange between a rhodium catalyst and an octane C-H group as it was broken. By using two of the world’s most powerful X-ray flash sources, the X-ray laser SwissFEL and the X-ray synchrotron Swiss Light Source, they could follow the reaction from start to finish. The measurements exposed the light-induced activation of the catalyst within 400 femtoseconds (0.0000000000004 seconds) to the final C-H bond breaking after 14 nanoseconds (0.000000014 seconds).

The complex experimental data was interpreted by theoreticians from Uppsala University and Stockholm University using advanced quantum-chemical calculations. These calculations identified how electronic charge flows between the metal catalyst and the C-H group in just the right amount. The study successfully demystifies a forty-year-old puzzle about how an activated catalyst can actually dismantle robust C-H bonds through careful electron exchange, without the need for high temperatures or pressures. With this new tool, the researchers aim to learn how to direct the flow of electrons and develop more effective catalysts for the chemical industry to make useful products out of methane and other alkanes.

This study is a continuation of the pioneering work of Manne, Kai, and Per Siegbahn. Manne Siegbahn, who won the Nobel Prize in Physics in 1924, was a pioneer in distinguishing different elements using X-rays. Kai Siegbahn, also a Nobel laureate in Physics in 1981, was at the forefront of distinguishing different chemical environments of the same element using X-rays. Per Siegbahn theoretically predicted the concerted exchange of electronic charge required to break a C-H bond.

Reference: “Tracking C-H activation with orbital resolution” by Raphael M. Jay, Ambar Banerjee, Torsten Leitner, Ru-Pan Wang, Jessica Harich, Robert Stefanuik, Hampus Wikmark, Michael R. Coates, Emma V. Beale, Victoria Kabanova, Abdullah Kahraman, Anna Wach, Dmitry Ozerov, Christopher Arrell, Philip J. M. Johnson, Camelia N. Borca, Claudio Cirelli, Camila Bacellar, Christopher Milne, Nils Huse, Grigory Smolentsev, Thomas Huthwelker, Michael Odelius and Philippe Wernet, 1 June 2023, Science. DOI: 10.1126/science.adf8042

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