钙钛矿LaMnO3负载贵金属在催化氧化碳烟中的作用

采用共沉淀法制备钙钛矿LaMnO₃,并用浸渍法在LaMnO₃上负载不同的贵金属得到系列催化剂.利用程序升温氧化反应对催化剂催化氧化碳烟的性能进行了测试.程序升温还原(H₂-TPR)、BET、XRD、SEM和FT-IR等表征手段对催化剂进行了表征.结果表明,当Pd的负载量在0.5%时,催化剂Pd/LaMnO₃的催化性能最好,和单独的LaMnO₃相比,最高燃烧速率温度降低了40℃.当负载量较小和较多时,碳烟起燃温度反而会比LaMnO₃高.在5种贵金属负载的催化剂中,其中Pd催化性能最好,依次为Au、Ru、Pt和 Rh.TPR测试表明贵金属的负载有助于钙钛矿中Mn⁴⁺的还原,对高温时Mn³⁺的还原作用不大.XRD衍射角向低角度出现了少许偏移,显示负载在表面的贵金属部分进入钙钛矿LaMnO₃的晶格结构中,使其晶粒增大;BET和SEM结果表明催化剂在反应后出现了轻微团聚现象.IR图谱显示反应前后,主要特征红外吸收带没有明显变化, 表明催化剂具有较好的结构稳定性.适量的贵金属在钙钛矿LaMnO₃上负载,能够有效地提高催化燃烧碳烟的活性.

Effect of Precious Metal Loaded on LaMnO3 on Catalytic Oxidation of Soot

Perovskite-type LaMnO3 catalysts were prepared by co-precipitation, and a series of precious metal-coating LaMnO3 catalysts were obtained by impregnation. The activity of catalysts on soot was tested by temperature-programmed reaction. Catalysts were characterized by techniques such as H2-TPR, BET, XRD, SEM and FT-IR. The activity of Pd/LaMnO3 coating 0.5% (weight) Pd is the optimal, and the maximum combustion rate temperature decreases about 40 degrees C , as compared with LaMnO3. When the coating amount is more or less than 0.5%, the ignition temperature is higher than that of pure LaMnO3. The activity of Pd/LaMnO3 is the highest among 5 precious metals-loading catalysts, and the sequence is Au,Ru,Pt and Rh. TPR experiments indicate precious metal can help the transformation of Mn4+ to Mn3+, but has less influence on reduction of Mn3+ to Mn2+ of LaMnO3. The downshift of diffraction angle of XRD indicates some precious metals enter crystal lattice of LaMnO3, the crystal sizes of catalysts become larger after precious metal loading; BET and SEM results show sintering happened to catalysts after catalytic reaction. No obvious changes occur in the IR spectra of catalysts between after and before reaction, indicating catalysts have good structural stability. In conclusion, proper amount precious metal coating on LaMnO3 effectively improve the catalytic activity of LaMnO3 on soot.