Scientists solve 40-year-old mystery of C-H bond breaking

Scientists have made significant progress in developing catalysts to convert the greenhouse gas methane into a less harmful substance. Their findings, published in the journal Science, shed light on how carbon-hydrogen bonds break and the mechanism behind catalysts in this process.

Methane, a potent greenhouse gas, is increasingly being released into the atmosphere through livestock farming and the thawing of permafrost. Converting methane and longer-chain alkanes into more useful and less harmful chemicals would mitigate these environmental threats and provide a valuable resource for the chemical industry. However, breaking the strong C-H bond, one of nature’s toughest chemical linkages, is a crucial first step in methane transformation.

Forty years ago, researchers discovered molecular metal catalysts capable of easily breaking C-H bonds. These catalysts only required a short flash of visible light to activate and effortlessly break the robust C-H bonds of alkanes. Despite the significance of this C-H activation reaction, the precise mechanism behind the catalyst’s function remained unknown.

A team of scientists from Uppsala University, in collaboration with the Paul Scherrer Institute in Switzerland, Stockholm University, Hamburg University, and the European XFEL in Germany, conducted groundbreaking research to directly observe the catalyst in action and uncover how it breaks C-H bonds.

Through two experiments conducted at the Paul Scherrer Institute in Switzerland, the researchers closely monitored the electron exchange between a rhodium catalyst and an octane C-H group as it underwent breaking. They utilized two of the world’s most powerful sources of X-ray flashes, the X-ray laser SwissFEL and the X-ray synchrotron Swiss Light Source, to track the reaction from start to finish. The measurements revealed that the catalyst’s light-induced activation occurs within 400 femtoseconds (0.0000000000004 seconds), leading to C-H bond breaking after 14 nanoseconds (0.000000014 seconds).

Raphael Jay, a researcher at Uppsala University and the lead experimentalist of the study, emphasized the significance of large-scale facilities like SwissFEL and the Swiss Light Source in enabling their time-resolved X-ray absorption experiments. By adopting the metal’s perspective, they could selectively identify the specific C-H bond that breaks out of hundreds of thousands present in the dense octane solution.

To interpret the intricate experimental data, theoreticians from Uppsala University and Stockholm University collaborated to perform advanced quantum-chemical calculations. Their calculations provided insights into the precise flow of electronic charge between the metal catalyst and the C-H group. They observed how charge transfer from the metal to the C-H bond establishes a connection between the two chemical groups, while charge transfer in the opposite direction acts as a scissor, ultimately separating the C and H atoms.

This study resolves a four-decade-old mystery surrounding the mechanism by which an activated catalyst breaks strong C-H bonds through controlled electron exchange, eliminating the need for extreme temperatures or pressures. Equipped with this newfound understanding, the researchers aim to explore how to manipulate the flow of electrons to develop improved catalysts for the chemical industry, enabling the transformation of methane and other alkanes into valuable products.

Spurce: Uppsala University

Leave a Comment