Nanoparticles powered by light aim to reduce chemical industry's carbon footprint

The carbon footprint in the chemical industry is likely to reduce as engineers from Rice University have invented a light-powered nanoparticle to help the cause. They are tiny spheres of copper dotted with single atoms of ruthenium, is the prime ingredient in composing a green process for developing synthesis gas, commonly known as syngas, the valuable chemical feedstock generally used to make fertilizer, fuels, and many other products. Researchers from Rice, UCLA and the University of California, Santa Barbara (UCSB), describe the low-energy, low-temperature syngas production process this week in Nature Energy. “Syngas can be made in many ways, but one of those, methane dry reforming, is increasingly important because the chemical inputs are methane and carbon dioxide, two potent and problematic greenhouse gases,” said Rice chemist and engineer Naomi Halas, a co-corresponding author on the paper. [caption id=“attachment_7898641” align=“alignnone” width=“1280”] Cranes stand at the construction site for a power plant in the US, 25 Feb 2014. Image: AT[/caption] Syngas is a mix of carbon monoxide and hydrogen gas that can be made from coal, biomass, natural gas and other sources. It’s produced at hundreds of gasification plants worldwide and is used to make fuels and chemicals worth more than $46 billion per year, according to a 2017 analysis by BCC Research. Catalysts, materials that spur reactions between other chemicals, are critical for gasification. Gasification plants typically use steam and catalysts to break apart hydrocarbons. The hydrogen atoms pair up to form hydrogen gas, and the carbon atoms combine with oxygen in the form of carbon monoxide. In dry reforming, the oxygen atoms come from carbon dioxide rather than steam. But dry reforming hasn’t been attractive to industry because it typically requires even higher temperatures and more energy than steam-based methods, said study first author Linan Zhou, a postdoctoral researcher at Rice’s Laboratory for Nanophotonics (LANP). Halas, who directs LANP, has worked for years to create light-activated nanoparticles that insert energy into chemical reactions with surgical precision. In 2011, her team showed it could boost the amount of short-lived, high-energy electrons called “hot carriers” that are created when light strikes metal, and in 2016 they unveiled the first of several “antenna reactors” that use hot carriers to drive catalysis. One of these, a copper and ruthenium antenna reactor for making hydrogen from ammonia, was the subject of a 2018 Science paper by Halas, Zhou and colleagues. Zhou said the syngas catalyst uses a similar design. In each, a copper sphere about 5-10 nanometers in diameter is dotted with ruthenium islands. For the ammonia catalysts, each island contained a few dozen atoms of ruthenium, but Zhou had to shrink these to a single atom for the dry reforming catalyst. Zhou said the question is important for producers, because most gasification catalysts are prone to “coking,” a buildup of surface carbon that eventually renders them useless. “They cannot change the catalyst every day,” Zhou said. “They want something that can last.” By isolating the active ruthenium sites where carbon is dissociated from hydrogen, Zhou reduced the chances of carbon atoms reacting with one another to form coke and increased the likelihood of them reacting with oxygen to form carbon monoxide. “But single-atom islands are not enough,” he said. “For stability, you need both single atoms and hot electrons.” Zhou said the team’s experimental and theoretical investigations point to hot carriers driving hydrogen away from the reactor surface. Halas said the research could pave the way “for sustainable, light-driven, low-temperature, methane-reforming reactions for production of hydrogen on demand.” “Beyond syngas, the single-atom, antenna-reactor design could be useful in designing energy-efficient catalysts for other applications,” she said. The technology has been licensed by Syzygy Plasmonics, a Houston-based startup whose co-founders include Halas and study co-author Peter Nordlander. Halas is Rice’s Stanley C Moore Professor of Electrical and Computer Engineering and professor of chemistry, bioengineering, physics and astronomy, and materials science and nanoengineering. Nordlander is the Wiess Chair and Professor of Physics and Astronomy, and professor of electrical and computer engineering, and materials science and nanoengineering.