铈铁锆三元复合氧化物上碳烟的催化燃烧
Catalytic combustion of soot on Ce-Fe-Zr-O ternary mixed oxide catalysts
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摘要: 采用水热法制备了纯CeO2、Fe2O3和系列Ce0.5Fe0.5-xZrxO2复合氧化物催化剂，采用XRD、Raman、H2-TPR和BET等方法对其进行了表征，并利用程序升温氧化反应(TPO)技术研究了其碳烟燃烧催化性能。结果表明，Zr4+完全进入CeO2晶格中形成了固溶体，而Fe3+较难进入CeO2晶格中，部分Fe2O3分散在固溶体表面。固溶体形成产生的氧空位和表面高度分散的氧化铁协同作用是铈铁锆三元复合氧化物具有较高碳烟燃烧催化性能的关键。同时，与单纯的铈铁二元复合氧化物相比，Zr4+的掺杂明显提高了催化剂的抗老化能力，使Ce0.5Fe0.5-xZrxO2复合氧化物显示出更好的应用前景。在系列样品中，Ce0.5Fe0.30Zr0.20O2样品由于形成了最多的固溶体并具有良好分散性的表面Fe2O3，显示出最好的催化活性和稳定性。其催化碳烟的起燃温度(ti)和峰顶温度(tp)分别为251℃和310℃，长时间高温老化后其ti和tp仍较低，分别为273℃和361℃。Abstract: Pure CeO2, Fe2O3 and a series of Ce0.5Fe0.5-xZrxO2 mixed oxide catalysts for soot catalytic combustion were prepared via hydrothermal method and characterized by XRD, Raman spectroscopy, H2-TPR and BET measurements. The catalytic activities in the diesel soot oxidation were tested by using temperature-programmed oxidation (TPO) reaction apparatus. The results show that all of the Zr4+ incorporated into the CeO2 lattice to form a solid solution. On the other hand, Fe3+ is extremely difficult to dissolve into the CeO2 lattice, and some Fe2O3 disperses on the surface of solid solution. The partial substitution of Ce4+ with Zr4+ and/or Fe3+ strongly improves the aging resistance of the catalysts. The strong synergetic effect between free Fe2O3 and surface oxygen vacancies wearies believed to have a pronounced positive effect on catalyst activity towards soot oxidation. Holding both the largest dopant content and well dispersed surfaceFe2O3, the Ce0.5Fe0.30Zr0.20O2 catalyst presents the lowest ti (251℃, ignition temperature of soot oxidation) and tp (310℃, temperature of maximum evolution of CO2). Even after aging for a long period at high temperature, the ti and tp values for Ce0.5Fe0.30Zr0.20O2 catalyst are still relatively low, at 273℃ and 361℃, respectively.
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