(60f) Characteristics of Pt-BaO/Mgal Mixed Oxides for NOx Storage-Reduction Catalysis

Efficient NOx abatement catalyst operated under lean condition must be developed to promote the use of more fuel-efficient diesel and/or lean-burn engines since conventional three-way catalyst does not work properly. For this purpose, selective catalytic reduction (SCR) catalyst or NOx storage-reduction (NSR) catalyst were commercially being used. NSR technology, which is more appropriate for the small-sized engine, primarily consisted of noble metals such as Pt, alkali earth metal (e.g. Ba) and support (e.g. Al₂O₃ or MgAl₂O₄).  It was demonstrated that MgAl₂O₄ support provided the improved NOx storage activity at higher temperature compared with Al₂O₃ support, implying that support material can play a crucial role in affecting the stability of barium nitrate species.

Hydrotalcite (HT) material, which can be precursors to MgAl₂O₄ spinel structure, has received more attention due to its various advantages, such as large surface area, controllable acid-base properties, and the improved thermal stability. In this work, HT materials with different Mg/Al ratios were prepared, resulting in the different amount of MgAl₂O₄ and Al₂O₃ in the support after calcination. Then, Pt-BaO active components were loaded on these HT-derived supports, and the catalysts were extensively investigated by using NOx storage measurement and various analytical techniques.  In addition, the effect of the promoter on the NOx storage activity in Pt-BaO/MgAl mixed oxides was also investigated.

Combination of activity measurement and characterization results indicates that MgAl mixed oxides supports give rise to the higher thermal stability of barium nitrates and Pt species as well as superior activity than one supported on Al₂O₃, moreover, can be optimized further for the high temperature NSR application by changing Mg/Al ratios in HT support.  This work provides fundamental understanding for optimizing HT-derived MgAl₂O₄ support, which would be a strong candidate for the high temperature NSR application.