Effect of Mg/Al ratios on the NOx storage activity over Pt-BaO/Mg–Al mixed oxides

• Pt-BaO/Mg-Al mixed oxide supports are applied for NOx storage-reduction catalysis.
• Mg–Al mixed oxides with various Mg/Al ratios from 1:9 to 5:5 are synthesized and used as support.
• Pt-BaO/Mg–Al mixed oxide support with Mg/Al ratio of 4:6 demonstrates the highest NOx storage activity and thermal stability.
• The optimized addition of Mg to Al aids in dispersing Pt and preventing thermal deterioration.

This study provides information on the optimal Mg/Al ratio to use Mg–Al mixed oxide as a support for NSR (NOx storage-reduction) catalysis. When Pt and Ba were loaded, Mg–Al mixed oxide support showed superior NOx storage performance compared with γ-Al2O3 supported catalyst, especially when Mg/Al ratio ranges from 2:8 to 4:6. In addition to the intrinsic superior activity of the fresh catalysts, we confirmed the positive effects of containing Mg in thermally aged catalysts, such as better thermal durability due to the minimized Pt sintering and less crystalline BaAl2O4 phase formation, thus demonstrating better overall NOx storage activity. In particular, among the catalysts with various Mg/Al ratios, Pt-BaO/Mg–Al mixed oxide support with the Mg/Al ratio of 4:6 showed the highest NOx storage performance after thermal treatment at 800 °C. However, the additional Mg loading to the support (Mg/Al ≥ 5:5) gave rise to the drastic decrease in the NOx storage activity and the poor thermal stability. Combined activity measurements and the physicochemical characterization results lead us to the conclusion that the use of optimized Mg–Al mixed oxide support can aid in improving NOx storage activity and preventing thermal deterioration.

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