Naomi Halas, director of Rice University's Laboratory for Nanophotonics, is an engineer and chemist who's spent more than 25 years pioneering the use of light-activated nanomaterials. Source: Jeff Fitlow/Rice UniversitySyngas, or synthesis gas, is a chemical feedstock used to make fuels, fertilizer and many other products. It is a mix of carbon monoxide and hydrogen gas made from coal, biomass, natural gas and other sources and is produced at hundreds of gasification plants worldwide.

Methane and carbon dioxide, two greenhouse gases, are chemical inputs for one method of producing syngas, known as methane dry reforming. This method is not often used because it requires even higher temperatures and more energy than other methods, which are also not environmentally friendly. Scientists at Rice University, however, have found a way to greatly reduce the carbon footprint of this important process.

The most common gasification methods use steam and catalysts to break apart hydrocarbons in order to form hydrogen gas and carbon monoxide. In dry reforming, oxygen atoms come from carbon dioxide rather than steam. The Rice engineers, along with researchers from UCLA and the University of California, Santa Barbara (UCSB), have developed a light-powered nanoparticle that acts as the catalyst for the chemical reaction. The nanoparticle, which consists of tiny spheres of copper and single atoms of ruthenium, is at the heart of a new low-energy, low-temperature syngas process.

The syngas catalyst uses a similar design to a copper and ruthenium antenna reactor for making hydrogen from ammonia that was the subject of an earlier paper by two of the team members, Naomi Halas and Linan Zhou. A copper sphere 5 to 10 nm in diameter is dotted with a single atom of ruthenium.

Stability and high efficiency are of major importance in this reaction. Gasification catalysts produce a buildup of surface carbon, known as "coking," which eventually causes them to stop working. By isolating the active ruthenium sites where carbon is dissociated from hydrogen, Zhou increased the likelihood of the carbon atoms reacting with oxygen to form carbon monoxide rather than reacting with each other to form coke. To accomplish this, he said, requires both single atoms and hot electrons. The team's work indicates that hot carriers drive hydrogen away from the reactor surface.

"When hydrogen leaves the surface quickly, it's more likely to form molecular hydrogen," he said. "It also decreases the possibility of a reaction between hydrogen and oxygen, and leaves the oxygen to react with carbon" and prevents it from forming coke.

Halas believes this discovery could lead to "sustainable, light-driven, low-temperature, methane-reforming reactions for production of hydrogen on demand," as well as for designing energy-efficient catalysts for other applications.

The technology is licensed by Syzygy Plasmonics, a Houston-based startup whose co-founders include Halas and study co-author Peter Nordlander.

This green syngas process is explained in Nature Energy.