Scientists have long debated how palladium works as a catalyst, mainly because it can act in two different ways—either in a solution or on the surface of nanoparticles. The difference between these two modes becomes less clear at the tiny nanoscale.
For the first time, researchers at the University of Nottingham’s School of Chemistry filmed the real-time growth and contraction of Palladium nanoparticles using transmission electron microscopy (TEM).
They observed the entire lifecycle of palladium nanoparticles in a liquid environment. The nanoparticles switch from nucleation through growth to dissolution, and this cycle repeats multiple times.
As the palladium nanoparticles can switch between these modes, it could lead to better catalysts for eco-friendly reactions like reducing carbon dioxide or making ammonia. This finding may also help in recycling palladium, a critical metal with a limited global supply.
Professor Andrei Khlobystov leads the research group at the University of Nottingham that focuses on imaging chemical reactions of individual molecules and atoms in real time and direct space. He says, “We set out to study the formation of palladium nanoparticles in a liquid and were happy to observe the nanoparticles forming directly during TEM observation.”
“These nanoparticles emerged from the palladium salt solution, growing larger and more structured over time. To our astonishment, once the nanoparticles reached a size of about 5 nanometres, they began to dissolve back into the solution, disappearing completely, only to undergo re-growth again.”
Within liquid, the nanoparticles form a complex branching pattern—they pulsate periodically while growing and dissolving. Conducting the same experiment in a carbon nanotube slows down the rate of chemical oscillations, allowing one to observe the lifecycle of the nanoparticles at atomic resolution.
Dr. Will Cull, a Research Fellow at the School of Chemistry, University of Nottingham, said: “The key to understanding this unexpected phenomenon lies in recognizing that electron microscopy is a powerful imaging technique that can also alter the material being observed.”
“In this case, the energy of the electron beam is harnessed to break carbon-hydrogen bonds and displace valence electrons from the bromide anions in the solvent. As a result, chemical reactions are triggered while we image our sample.”
According to researchers, the electron beam activated the chemical reactions involving the solvent. It drove the reduction of palladium ions to palladium metal and the oxidation of palladium metal back to palladium ions.
Because of the competition between these two processes, the nanoparticles continuously grow and shrink, oscillating chemically between these two states.
Journal Reference
- Rhys W. Lodge, William J. Cull, Andreas Weilhard et al. A nanoscale chemical oscillator: reversible formation of palladium nanoparticles in ionic liquid. Nanoscale. DOI: 10.1039/D4NR04150J
Source: Tech Explorist
