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An X-ray flash illuminates a molecule. Credit: Raphael Jay

Topics: Chemistry, Climate Change, Green Tech, High Energy Physics, Research, X-rays

The use of short flashes of X-ray light brings scientists one big step closer to developing better catalysts to transform the greenhouse gas methane into a less harmful chemical. The result, published in the journal Science, reveals for the first time how carbon-hydrogen bonds of alkanes break and how the catalyst works in this reaction.

Methane, one of the most potent greenhouse gases, is being released into the atmosphere at an increasing rate by livestock farming and the unfreezing of permafrost. Transforming methane and longer-chain alkanes into less harmful and, in fact, useful chemicals would remove the associated threats and, in turn, make a huge feedstock for the chemical industry available. However, transforming methane necessitates, as a first step, the breaking of a C-H bond, one of the strongest chemical linkages in nature.

Forty years ago, molecular metal catalysts that can easily split C-H bonds were discovered. The only thing found to be necessary was a short flash of visible light to "switch on" the catalyst, and, as by magic, the strong C-H bonds of alkanes passing nearby are easily broken almost without using any energy. Despite the importance of this so-called C-H activation reaction, it remained unknown over the decades how that catalyst performs this function.

The research was led 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, the scientists were able to directly watch the catalyst at work and reveal how it breaks those C-H bonds.

In two experiments conducted at the Paul Scherrer Institute in Switzerland, the researchers were able to follow the delicate exchange of electrons between a rhodium catalyst and an octane C-H group as it gets broken. Using two of the most powerful sources of X-ray flashes in the world, the X-ray laser SwissFEL and the X-ray synchrotron Swiss Light Source, the reaction could be followed all the way from the beginning to the end. The measurements revealed the initial 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).

X-rays visualize how one of nature's strongest bonds breaks, Uppsala University, Phys.org.

Figure 1. Sarah Frances Whiting (1847–1927) using a fluoroscope to examine the bones in her hand in Wellesley College’s physics laboratory, circa 1896. On the table in front of her is a Crookes tube mounted on a stand and an induction coil to modulate the voltage. (Courtesy of Wellesley College.)

Topics: Applied Physics, Optics, Women in Science, X-rays

In February 1896 Sarah Frances Whiting, founder of the physics and astronomy departments at Wellesley College, conducted a series of x-ray experiments. She was working only a few weeks after the public announcement of Wilhelm Röntgen’s discovery of the rays, and she was not alone; amateur and professional scientists at colleges, universities, and medical centers across the US were attempting to replicate and extend Röntgen’s results. But Whiting (see figure 1), who enlisted the assistance of a Wellesley colleague and several students, was among the first to do so successfully. Even more importantly, Whiting was the first woman—and almost certainly the first person, male or female—to do so in an undergraduate laboratory. Her original glass plates from the experiments do not survive, but 15 photographs printed from them (see the opening image of one such photo above) were recently rediscovered in a campus building slated for demolition. They provide a vivid reminder of Whiting’s success.

The x-ray experiments were only one instance in which Whiting drew on her keen engagement with contemporary scientific advances to offer her students an experience available to few undergraduates at the time, and to almost no women. Throughout her long career, Whiting introduced thousands of women to physics and astronomy, both fields then associated almost entirely with men. Her pedagogical efforts led many of her female students to pursue their own careers in the sciences.

Sarah Frances Whiting and the “photography of the invisible”

John S. Cameron is an emeritus professor of biological sciences and Jacqueline Marie Musacchio is a professor of art history at Wellesley College in Massachusetts.