Researchers have discovered a metastable state that explains why a platinum catalyst can be active below its threshold temperature. Platinum is a central component of many catalysts, including those used in cars, where it promotes the oxidation of toxic carbon monoxide into carbon dioxide. This process typically only occurs when the platinum reaches a threshold temperature. However, some platinum catalysts are already active even when the required temperature has not been reached. Researchers at the Technical University of Vienna investigated the cold reaction of platinum to understand this phenomenon.
The team used a scanning tunneling microscope to examine the smallest possible platinum catalyst, consisting of a layer of individual platinum atoms on an iron oxide substrate. The researchers gradually increased the temperature and introduced carbon monoxide to observe the reaction. They found that the platinum atoms already had their catalytic function at 277 degrees Celsius, a much lower temperature than previously predicted. The researchers observed that two platinum atoms formed a pair, each holding onto a carbon monoxide molecule. These platinum-carbon monoxide bridges were clearly visible in the microscope images.
The unexpected aspect of this mechanism is that both the platinum-carbon monoxide dimer and the iron oxide support take on a metastable state that enables the reaction. The substrate then releases an oxygen atom during the catalytic reaction, which combines with the carbon monoxide molecule to form carbon dioxide. The platinum dimers then release a carbon dioxide molecule before breaking down into two adatoms and releasing the second carbon dioxide molecule. This observation shows a metastable state that allows a platinum catalyst to be active at temperatures well below its threshold. By incorporating these short-term states into computer simulations, researchers can achieve results that match experimental measurements.
