Effect of TiO2 on the Reduction Performance of NOx Storage and Reduction Catalysts for Lean-burn Natural Gas Vehicle

The effect of TiO₂ on the reduction performance of NSR catalysts is investgated for lean-burn natural gas vehicles applications. 3 types of NSR catalysts containing various amount of TiO₂ are prepared to reduce NOx from the natural gas vehicle. In NSR catalysts, the main catalysts are composed of precious metals, Pt, Pd, Rh, and barium(Ba) which was used to adsorb the NOx in a lean engine condition. The catalytic reactions on NOx storage and reduction were estimted with the synthetic model gases. To examine the catalytic deactivation, the catalysts were aged under a laboratory hydrothermal aging mode. The characterizations of fresh and aged catalysts were carried out by SEM, TEM, and NO-TPD. It was found that the addition of TiO₂ in the NSR catalyst decreased a little bit of the NOx adsorption in comparison to the NSR catalyst without TiO₂. At the catalyst temperature of 400 °C, the NOx reduction ratio of the fresh NSR catalyst containing 3.0 g/L TiO₂ was almost the same level comparing with the NSR catalyst without TiO₂. The amount of NOx adsorption of the aged NSR catalyst containing TiO₂ increases a little comparing with the NSR catalyst without TiO₂. The NOx reduction ratio of NSR catalyst is almost an equal level comparing to the NSR catalyst without TiO₂. Therefore, we suggest that the optimum amount of TiO₂ loaded to NSR catalyst should be about 3.0 g/L to increase durability of the NSR catalyst.