SHIRAI Laboratory's research paper, "Insights into the selective reduction of NO over Al₂O₃-supported Pt, Rh, and Pd catalysts," which elucidates a new reaction mechanism for nitrogen oxide removal in automotive exhaust purification catalysts, has been highly acclaimed and selected for the Outside Front Cover of Catalysis Science & Technology, a journal published by the Royal Society of Chemistry in the United Kingdom.

Nitrogen oxides (NO_x) are air pollutants generated during high-temperature combustion processes, such as those in automobile engines and industrial furnaces. They are known to cause photochemical smog and acid rain, and emission regulations are being tightened around the world. Meanwhile, depending on the exhaust gas purification technology used, nitrous oxide (N₂O), a greenhouse gas, may be produced as a by-product, posing a new challenge from the perspective of climate change mitigation. N₂O is known not only to have a far greater greenhouse effect than carbon dioxide (CO₂), but also to contribute to ozone layer depletion.

In this study, the researchers conducted a detailed analysis of the NO purification reaction using hydrogen as a reducing agent over alumina-supported catalysts containing platinum (Pt), palladium (Pd), and rhodium (Rh) nanoparticles. In particular, they focused on the formation mechanisms of N₂O and ammonia (NH₃), which are generated as by-products during the reaction, with the aim of obtaining fundamental insights for achieving both high exhaust purification performance and reduced environmental impact.

As a result, the study revealed that Rh catalysts can significantly reduce the formation of N₂O and NH₃ by suppressing undesirable side reactions through the formation of stable chemical bonds with nitrogen oxides. Furthermore, by systematically clarifying the differences in reaction mechanisms among platinum-group metals, the study presents new guidelines for the design of next-generation exhaust purification.