NO_x储存-还原催化剂Pt-Pd/BaO/TiAlO的制备及其抗硫性能

Preparation of Pt-Pd/BaO/TiAlO Catalyst for NO_x Storage-Reduction and Its Sulfur Resistance

采用共沉淀-浸渍法制备了新型催化剂Pt-Pd/BaO/TiAlO,通过对催化剂进行NOx吸附储存实验、有硫(SO2)和无硫情况下的NOx储存-还原循环实验以及程序升温脱附、程序升温还原、N2吸附-脱附和X射线衍射等表征分析,考察了该催化剂的储存NOx性能以及抗硫性能.结果表明,在Pt-Pd/BaO/TiAlO中,复合氧化物TiAlO为储存NOx的组分兼载体,Ti和Al原子比为1∶2时,储存NOx能力最大;BaO(4%)作为助剂不但增加了催化剂的热稳定性,还提高了其储存NOx的能力.与Pt/BaO/γ-Al2O3相比,Pt-Pd/BaO/TiAlO具有良好的抗硫性能.Pt-Pd/BaO/TiAlO上吸附形成的硫化物稳定性较差,易被还原脱除,这是其抗硫性能良好的原因之一.

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 12 000 h^-1, 800 mg/m^3 of NO, 4% of 02, 200 mg/m3 of SOs for sulfur resistance test, remainder Ar, 350 ℃, and for 30 rain） to rich conditions （GHSV of 12 000 h-1, 4% of H2, remainder Ar, 350 ℃, and for 20 min）. The TiA10 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/A1 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.