Abstract: NOx in exhaust gases from lean burn engines can be clarified over Toyota-type storage-reduction catalysts, but it is difficult for the catalyst to be applied in domestic automobiles due to deterioration caused by SO2 in the emission. A novel Pt-Pd/BaO/TiAlO catalyst for NOx storage-reduction (NSR) was prepared by coprecipitation-impregnation. The catalyst was evaluated by NOx storage in lean burn and by NOx storage-reduction in lean-rich cycles both in the absence and in the presence of SO2, respectively, using a series cyclic sequences of feed which changes from lean conditions (GHSV of 12000 h-1, 800 mg/m3 of NO, 4% of O2, 200 mg/m3 of SO2 for sulfur resistance test, remainder Ar, 350 ℃, and for 30 min) to rich conditions (GHSV of 12000 h-1, 4% of H2, remainder Ar, 350 ℃, and for 20 min). The TiAlO bi-oxide and the catalyst were characterized by temperature-programmed desorption, temperature-programmed reduction, N2 adsorption-desorption, and X-ray diffraction. The results showed that TiAlO bi-oxide in Pt-Pd/BaO/TiAlO catalyst acted as both a support and an adsorbent in the NOx storage-reduction process. The maximum capacity for NOx storage was obtained when the molar ratio of Ti/Al in TiAlO was 1∶2. BaO (4%) not only enhanced the thermal stability of catalyst but also increased NOx storage capacity. Pt-Pd/BaO/TiAlO had better sulfur resistance compared with the Toyota-type NSR catalyst Pt/BaO/γ-Al2O3. One of the reasons might be that sulfur compounds produced in NOx storage on the surface of the catalyst were unstable and easily to be removed by reduction.

Key words: platinum, palladium, barium oxide, titanium-aluminum bi-oxide, nitrogen oxide, storage-reduction catalyst, sulfur resistance, lean burn engine emission