Researchers have unveiled a groundbreaking photocatalyst that can make steam methane reforming completely free of emissions while also enhancing the longevity of catalysts.
As a clean and efficient energy source, hydrogen has the potential to be a major player in the shift towards sustainable energy systems. However, the current method that generates over half of the global hydrogen supply contributes significantly to greenhouse gas emissions.
Researchers from Rice University have created a catalyst that could enable steam methane reforming (SMR) to operate without generating emissions by utilizing light instead of heat to facilitate the reaction. Additionally, this research may be pivotal in extending the lifespan of catalysts across various industrial processes, improving efficiency, and lowering costs, particularly in areas affected by coking, which is a carbon buildup that can impair catalyst function.
The innovative copper-rhodium photocatalyst features a design known as an antenna-reactor. When illuminated with a specific wavelength of light, it decomposes methane and water vapor into hydrogen and carbon monoxide without the need for external heating. Carbon monoxide serves as an important feedstock in the chemical industry and does not contribute to greenhouse gas emissions.
“This discovery is one of our most significant accomplishments to date, as it presents a better option for what might be the most crucial chemical process in modern society,” commented Peter Nordlander, who holds the Wiess Chair at Rice and is a professor of Physics and Astronomy, as well as Electrical and Computer Engineering and Materials Science. “We’ve established a completely new and more sustainable method for conducting SMR.”
Naomi Halas, a Rice University Professor and the Stanley C. Moore Professor of Electrical and Computer Engineering, along with Nordlander, are the principal authors of a study detailing this research, which has been published in Nature Catalysis.
This novel SMR approach builds on a discovery made in 2011 by Halas and Nordlander’s teams, which found that plasmons—collective oscillations of electrons that metal nanoparticles emit when exposed to light—can produce “hot carriers” or high-energy electrons and holes necessary for driving chemical reactions.
“We specialize in plasmonic photochemistry—plasmons are essential to our work—because they are highly effective light absorbers and can produce very energetic carriers that perform the required chemistry much more effectively than traditional thermocatalysis,” explained Yigao Yuan, a Rice doctoral student and the lead author of the study.
The new catalyst system employs copper nanoparticles to capture energy. However, since these copper nanoparticles do not bond well with methane, rhodium atoms were strategically placed as reaction sites. The rhodium aids in binding water and methane molecules to the plasmonic surface, utilizing the energy from hot carriers to drive the SMR process.
“After testing numerous catalyst systems, this one proved to be the most effective,” Yuan noted.
The findings also indicate that this antenna-reactor technology can mitigate catalyst deactivation caused by oxidation and coking by using hot carriers to eliminate oxygen and carbon residues, thereby regenerating the catalyst when exposed to light. Nordlander emphasized that the key to this “remarkable effect was the strategic irregular distribution of the rhodium,” which was sparsely applied across the surface of the nanoparticles.
Presently, hydrogen is largely produced in large, centralized plants, necessitating its transportation to where it is needed. In contrast, this light-driven SMR technique allows for hydrogen to be generated whenever needed, making it particularly beneficial for applications related to mobility, such as hydrogen fueling stations or even vehicles.
“This research highlights the potential of innovative photochemistry to transform essential industrial processes, bringing us closer to a sustainable energy future,” Halas remarked.
The research received support from the Robert A. Welch Foundation (C-1220, C-1222) and the Air Force Office of Scientific Research (FA9550-15-1-0022). Additionally, the Shared Equipment Authority at Rice contributed valuable insights and assistance with data analysis.
