Ce_(0.7)Zr_(0.3)O_(2)纳米棒的制备及其对柴油车尾气碳颗粒的催化净化性能

Preparation of Ce_(0.7)Zr_(0.3)O_(2)nanorod and its performances on catalytic soot purification from diesel exhaust

本研究以硝酸铈、硝酸锆为原料使用溶剂热合成法,制备了CeO_(2)-ZrO_(2)纳米棒催化剂(Ce_(0.7)Zr_(0.3)O_(2)(NR)),并用于柴油车尾气碳颗粒催化净化.催化活性检测证实:Ce_(0.7)Zr_(0.3)O_(2)(NR)纳米棒催化剂可有效净化柴油车尾气碳烟颗粒.在Ce_(0.7)Zr_(0.3)O_(2)(NR)存在下,碳颗粒净化率为10%、50%和90%时,所需温度分别仅为375℃、414℃和455℃,比商用Ce_(0.7)Zr_(0.3)O_(2)和Ce0.3Zr0.7O2催化剂性能更优.采用氮吸附-脱附、X射线光电子能谱(XPS)、H2程序升温还原(H_(2)-TPR)、X射线衍射(XRD)、拉曼光谱(Raman)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等技术对催化剂进行表征.XRD和Raman结果证实,Ce_(0.7)Zr_(0.3)O_(2)(NR)主要由立方相CeO_(2)构成,并掺杂了少量四方相氧化锆.SEM和TEM结果则显示,Ce_(0.7)Zr_(0.3)O_(2)(NR)催化剂颗粒明显由纳米棒堆积而成,特定的纳米形貌会影响其对碳颗粒的催化氧化活性.XPS结果证明Ce_(0.7)Zr_(0.3)O_(2)(NR)催化剂主要具有晶格氧、化学氧和表面吸附氧等氧物种;晶格氧是碳颗粒氧化的活性氧物种,其溢流到催化剂表面可与碳颗粒接触从而提高反应活性;化学氧和表面吸附氧均为表面氧物种,极易与表面固体碳颗粒直接接触,从而可在较低温度下促进碳颗粒的净化.H_(2)-TPR结果进一步证实了XPS结果,Ce_(0.7)Zr_(0.3)O_(2)(NR)催化剂的低温还原温度比商用Ce_(0.7)Zr_(0.3)O_(2)催化剂更低,且含有更多的易还原氧物种,这些低温易还原氧物种可以在较低温度下参与催化反应,促进柴油车尾气颗粒物的低温催化净化.

In this work,cerium nitrate hexahydrate and zirconium nitrate pentahydrate were used as raw materials to prepare CeO_(2)-ZrO_(2)nanorod catalyst(Ce_(0.7)Zr_(0.3)O_(2)(NR))by solvothermal method,and its performances on catalytic diesel soot purification were studied.The catalytic activity results showed that the Ce_(0.7)Zr_(0.3)O_(2)(NR)catalyst could effectively eliminate diesel soot particulates,and the temperature of soot conversion at 10%,50%and 90%were 375℃,414℃and 455℃,respectively.These values were obviously lower than the commercial Ce_(0.7)Zr_(0.3)O_(2)and Ce0.3Zr0.7O2 catalysts,which indicated that the prepared Ce_(0.7)Zr_(0.3)O_(2)(NR)catalyst had better catalytic diesel soot purification activity.All of the catalysts were characterized by N_(2)adsorption-desorption,X-ray photoelectron spectroscopy(XPS),H_(2)program-temperature reduction(H2-TPR),X-ray diffraction(XRD),Raman spectroscopy(Raman),scanning electron microscope(SEM)and transmission electron microscope(TEM).XRD and Raman results impled that the dominative crystalline phase of Ce_(0.7)Zr_(0.3)O_(2)(NR)was cubic phase,and comprise with little tetragonal zirconia.SEM and TEM results demonstrated that the morphology of Ce_(0.7)Zr_(0.3)O_(2)(NR)catalyst was nanorod,which would affect the catalytic activity for soot oxidation.XPS results showed that the Ce_(0.7)Zr_(0.3)O_(2)(NR)contained lattice oxygen,chemical oxygen and surface adsorption oxygen;lattice oxygen was active oxygen for soot oxidation,which could spill over onto the catalyst surface to form active oxygen species and hence improve the catalytic activity;both the chemical oxygen and surface adsorption oxygen were surface oxygen species which could easily contact with soot and promote the catalytic purification of soot at lower temperature.The H2-TPR results were in line with the XPS results,the Ce_(0.7)Zr_(0.3)O_(2)(NR)catalyst exhibited lower reduction temperature and more reducible oxygen species than the commercial Ce_(0.7)Zr_(0.3)O_(2)catalyst,which could participate in the catalytic soot oxidation reaction at lower temperature and hence promote low-temperature catalytic purification activity of diesel soot.