Breakthrough in Air Quality: Novel Catalyst Enables Near-Total Conversion of Harmful Carbon Monoxide at Ambient Temperatures
Researchers have shown that by altering the substrate material in catalytic converters, it is feasible to nearly fully transform noxious carbon monoxide into carbon dioxide, even at room temperature conditions. By concentrating on cerium oxide (ceria) as the substrate material and fine-tuning its crystal dimensions, the team was able to enhance the efficacy of precious metals, thereby paving the way for more effective catalysts.
A recent scientific paper details an innovative catalyst proficient in neutralizing exhaust pollutants at room temperature.
Traditional three-way catalytic converters in automotive exhaust systems rely on expensive components and operate optimally only when the exhaust reaches temperatures of several hundred degrees Celsius. As a result, during the initial ignition of a vehicle or when managing a hybrid car where the gasoline engine and electric motor alternate in providing power, the emitted gases can still encompass harmful carbon monoxide.
In a newly published article in the journal Science, a team of scientists led by Emiel Hensen has established that by modifying the substrate material of the catalytic converter, it becomes viable to nearly fully convert toxic carbon monoxide into safer carbon dioxide gas at ambient temperatures.
Essential Precious Metals
Catalysts used in the automotive sector are typically fabricated by layering precious metals such as platinum, palladium, and rhodium onto a base material made of cerium oxide (ceria). Due to the scarcity and costliness of these precious metals, global research is focusing on methods to attain comparable or superior catalytic performance while minimizing material usage.
In a prior publication, Hensen’s research group at TU/e demonstrated that distributing the precious metal as individual atoms could result not only in reduced material consumption but also in heightened catalytic efficiency under certain conditions.
A Shift in Perspective: Substrate Material
The research, led by Ph.D. candidate Valery Muravev, pivoted their focus from precious metals to the underlying substrate material, ceria, to further optimize catalyst performance. They fabricated ceria crystals in various sizes and deposited the precious metals in the form of single atoms concurrently. They then examined how effectively these material combinations were able to attach an additional oxygen atom to carbon monoxide molecules.
It was found that ceria crystals with dimensions of 4 nanometers significantly enhanced the performance of the precious metal palladium, especially under cold start conditions with a surplus of carbon monoxide. This enhanced performance was attributed to the increased reactivity of oxygen atoms at smaller ceria crystal sizes. In more typical conditions, ceria crystals of 8 nanometers were identified as the optimum size to achieve high catalytic activity at temperatures below 100 degrees Celsius.
Broader Implications
The study reveals for the first time that in the field of catalyst development, attention must be paid not solely to the active precious metals but also to the carrier materials. In this specific case, altering the particle sizes of the substrate material offers a promising avenue for further advancement of catalysts, thereby improving the efficiency and selectivity of chemical reactions. This has broader implications for developing processes that combine ambient carbon dioxide with green hydrogen for fuel production or the manufacturing of sustainable plastics.
The research team, in collaboration with British company Johnson Matthey, a leading producer of automotive catalysts, will continue to explore ways to translate these insights into marketable products.
Reference: “Size of cerium dioxide support nanocrystals dictates reactivity of highly dispersed palladium catalysts” by Valery Muravev, Alexander Parastaev, Yannis van den Bosch, Bianca Ligt, Nathalie Claes, Sara Bals, Nikolay Kosinov, and Emiel J. M. Hensen, published on June 15, 2023, in the journal Science.
DOI: 10.1126/science.adf9082
