Tender X-rays show how one of nature’s strongest bonds breaks

Short flashes of an unusual kind of X-ray light at SwissFEL and SLS bring scientists 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 as well as the continuing 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 available a huge feedstock for the chemical industry. 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 were discovered that can easily split C-H bonds. The only thing found to be necessary was a short flash of visible light to “switch on” the catalyst and – bafflingly – the strong C-H bonds of alkanes passing nearby were easily broken almost without using any energy. Despite the importance of this so-called C-H activation reaction, it has remained unknown how that catalyst performs this function. Now, experiments at Swiss FEL and SLS have enabled a research team led by scientists at Uppsala University to directly watch the catalyst at work and reveal how it breaks the C-H bonds.

Read more on the PSI website

Image: An X-ray flash illuminates a molecule

Credit: University of Uppsala / Raphael Jay

The problems with coal ash start smaller than anyone thought

How well toxic elements leach out of coal ash depends on the ash’s nanoscale composition

Everyone knows that burning coal causes air pollution that is harmful to the climate and human health. But the ash left over can often be harmful as well.

For example, Duke Energy long stored a liquified form of coal ash in 36 large ponds across the Carolinas. That all changed in 2014, when a spill at its Dan River site released 27 million gallons of ash pond water into the local environment. The incident raised concerns about the dangers associated with even trace amounts of toxic elements like arsenic and selenium in the ash. Little was known, however, about just how much of these hazardous materials were present in the ash water or how easily they could contaminate the surrounding environment.

Fears of future spills and seepage caused Duke Energy to agree to pay $1.1 billion to decommission most of its coal ash ponds over the coming years. Meanwhile, researchers are working on better ways of putting the ash to use, such as recycling it to recover valuable rare earth elements or incorporating it into building materials such as concrete. But to put any potential solution into action, researchers still must know which sources of coal ash pose a hazardous risk due to its chemical makeup — a question that scientists still struggle to answer.

In a new paper published June 6 in the journal Environmental Science: Nano, researchers at Duke University have discovered that these answers may remain elusive because nobody is thinking small enough. Using one of the newest, most advanced synchrotron light sources in the world — the National Synchrotron Light Source II at Brookhaven National Laboratory — the authors show that, at least for selenium and arsenic, the amount of toxic elements able to escape from coal ash depends largely on their nanoscale structures.

Read more on the BNL website

Image: Leftover sludge from the 2008 coal ash spill at the Kingston TVA power plant. New research indicates that the nanoscale structure of the coal ash plays a large part in whether or not toxic chemicals can leach into the environment from such events