Home Career Consideration of the dynamics of oxygen accumulation in three-way catalysts — ScienceDaily

Consideration of the dynamics of oxygen accumulation in three-way catalysts — ScienceDaily

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With car pollutants contributing to lower air quality, governments around the world are imposing stricter regulations on car emissions. This requires the development of more efficient exhaust gas aftertreatment systems (ie, systems to “clean” exhaust gases before they are released into the atmosphere). The most common way to treat the exhaust gases of gasoline-powered internal combustion engines is through three-way catalytic converters (TWCs) or catalytic converters. TWCs often contain active metals such as platinum (Pt) and palladium (Pd) nanoparticles and high surface area oxygen storage materials such as CeO solid solution2-ZrO2(CZ). These components can catalyze numerous oxidation and reduction reactions that can convert harmful car engine exhaust gases into harmless gases.

The durability, accuracy, and performance of TWCs depends on factors such as the oxygen stored or removed from the volume and surface of the oxygen storage materials. Therefore, a clear understanding of the oxygen transport and dynamics of the storage material is necessary to improve its efficiency. Unfortunately, there is a lack of methods to directly monitor the oxygen storage process in TWC.

In a recent breakthrough published in Journal of Chemical Engineering, however, a group of researchers led by Associate Professor Tsuyoshi Nagasawa of the Tokyo Institute of Technology (Tokyo Tech) presented a solution to the problem. The team developed a new technique for direct imaging of the oxygen storage process in Pd/CZ TWCs using the isotope quenching technique. Professor Nagasawa explains: “It is difficult to gain clarity on the dynamic interactions – such as oxygen adsorption/desorption and surface/bulk diffusion – that occur on TWC surfaces, because they can only be assessed indirectly from changes in the valence of cerium in CZ or the oxidation state of the noble metal .However, our method overcomes these problems by incorporating quenched isotope labeling, allowing us to investigate oxygen storage processes by tracking 18The O isotope involved in these interactions.”

How was this isotope quenching technique carried out? The team prepared a TWC model consisting of the precious metal Pd and a dense CZ substrate, which is preserved 18O2 in it at 600 °C and then quench the catalyst using two helium nozzles covered by a water cooling jacket. They then used high-resolution secondary ion mass spectrometry to analyze it 18Surface and bulk distribution of Pd/CZ.

The results showed that Pd improves the depth of diffusion 18O in the volume of CZ, as well as its concentration on the surface. Then it turned out that 18O is preferentially adsorbed at the Pd/CZ interface compared to the Pd center, where its concentration was lower. Density functional theory calculations also agreed with these observations.

Finally, the team calculated local oxygen release/storage rates by comparison 18Modeling oxygen distribution and release/storage using the diffusion equation. They found that local readings were comparable and consistent with conventional measurements of oxygen storage capacity.

This new imaging process provides useful information on the mechanisms of oxygen storage and release in metal/oxygen materials systems and can be used to further investigate and improve the performance and efficiency of TWCs used for automotive exhaust gas treatment. “Volatile organic compounds and oxides of nitrogen and carbon, which are commonly produced by internal combustion engines, if released untreated, can not only cause respiratory health problems, but can also indirectly contribute to the acceleration of global warming. With our research, we wanted to contribute to the global mission to achieve better emissions practices,” Professor Nagasawa concludes.

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Materials is provided Tokyo Institute of Technology. Note: Content can be edited for style and length.

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