Catalysts open the way for chemical reactions to unfold at faster and more efficient rates, and the development of new catalytic technologies is an important part of the green energy transition.
Naomi Halas, a pioneer in Rice University's Nanotechnology Laboratory, has discovered an innovative approach to harnessing the catalytic power of aluminum nanoparticles by annealing them in various gas atmospheres at high temperatures.
According to a study published in Publications of the National Academy of SciencesRice researchers and collaborators show that changing the structure of the oxide layer that coats the particles can modify the catalyst properties, making it a versatile tool that can be tailored to the needs of a variety of use situations, from sustainable fuel production to water production. I showed it. Based reaction.
“Aluminum is an earth-abundant metal used in many structural and technological applications,” said Aaron Bayles, lead author of the paper and Rice PhD graduate. “All aluminum is coated with a surface oxide, and until now we did not know what the structure of the native oxide layer on top of the nanoparticles was. This was a limiting factor preventing the widespread application of aluminum nanoparticles.”
Aluminum nanoparticles absorb and scatter light with remarkable efficiency due to surface plasmon resonance (the collective oscillation of electrons on a metal surface in response to light of a specific wavelength). Like other plasmonic nanoparticles, aluminum nanocrystal cores can act as nanoscale optical antennas, making them promising catalysts for light-based reactions.
“Almost all the chemicals we use every day, all the plastics, come from catalytic processes, and many of those catalytic processes rely on precious metals like platinum, rhodium, ruthenium, etc.,” Bayles said.
“Our ultimate goal is to revolutionize catalysis to make it more accessible, efficient and environmentally friendly,” said Halas, the highest-ranking university professor at Rice University. “By harnessing the potential of plasmonic photocatalysis, we are paving the way for a brighter, more sustainable future.”
The Halas group has been developing aluminum nanoparticles for plasmonic photocatalytic reactions, such as the decomposition of hazardous chemical warfare agents and the efficient production of commercial chemicals. The newly discovered ability to modify the surface oxides of aluminum nanoparticles further increases their versatility for use as catalysts to efficiently convert light into chemical energy.
“When performing a catalytic reaction, the molecules of the material you are trying to convert interact with the aluminum oxide layer and not with the aluminum metal core, but that metal nanocrystal core is uniquely capable of absorbing light very efficiently, and while converting it into energy, the oxide layer It acts as a reactor, transferring that energy to the reactant molecules, Bayles said.
The properties of a nanoparticle's oxide coating determine how the nanoparticle interacts with other molecules or materials. The study reveals the native oxide layer structure of aluminum nanoparticles and shows that the structure can be altered by simple heat treatments (e.g., heating the particles up to 500 degrees Celsius (932 Fahrenheit) in various gases).
“Crystal phase, intragranular strain and defect density can all be modified with this simple approach,” Bayles said. “At first I was convinced that heat treatment had no effect, but the results surprised me.”
One of the effects of the heat treatment was to make it easier for the aluminum nanoparticles to convert carbon dioxide into carbon monoxide and water.
Changing the alumina layer in this way affects its catalytic properties, particularly for light-assisted carbon dioxide reduction, meaning the nanoparticles could be useful in producing sustainable fuels, according to the National Renewable Energy Laboratory. said Bayles, a postdoctoral researcher at the Energy Laboratory. .
“The ability to use abundant aluminum instead of precious metals could have a major impact in combating climate change and paves the way for other materials to be similarly improved,” Bayles added.
“It was relatively easy to perform this treatment and get a large change in catalyst behavior, which is surprising because aluminum oxide is famous for being unreactive – it’s very stable,” Bayles said. “So for materials that are a little more reactive, like titanium oxide or copper oxide, you might see a bigger effect.”
This research was supported by the Air Force Office of Scientific Research (FA9550-15-1-0022), the Defense Threat Reduction Agency (HDTRA1-16-1-0042), the National Science Foundation (1449500, 1905757, 2239545), and the Robert A. Welch Foundation (C-1220). , C-1222, C-2065), Department of Defense SMART Scholarship and Fulbright Colombia-Pasaporte a la Ciencia.