纳米级V_2O_5/TiO_2的活性特征及对碳烟氧化的催化作用

Active Features of Nano-Scale V_2O_5/TiO_2 Catalyst and Its Effect on Soot Oxidation

采用浸渍法制备了不同钒负载量的纳米级V_2O_5/TiO_2催化剂,通过扫描电镜(scanning electron microscope,SEM)、X射线衍射仪(X-ray diffractomer,XRD)和傅里叶红外光谱(Fourier transform infrared spectrometer,FT-IR)测试手段对催化剂的物化特性进行表征。以Printex-U碳黑作为实际发动机颗粒的替代物,利用热重分析法探究V_2O_5负载量对催化氧化碳烟活性的影响,并基于Flynn-Wall-Ozawa法定量表征碳烟催化氧化反应过程。研究结果表明:较低钒负载量时,活性组分钒氧物种处于高度分散状态,基本呈现单层分布。当负载量较高(40%)时,部分钒氧物种开始团聚并以结晶态析出,催化剂表面出现明显的柱状晶结构。随着钒负载量的增加,在碳烟氧化过程中催化剂活性呈递增趋势。在一系列样品中,负载量20%的V_2O_5/TiO_2催化剂表现出最佳催化活性,与无触媒状态相比,碳烟氧化的起燃温度Ti、失重峰值温度Tp和燃尽温度Tf等特征温度的降幅最大。当负载量达40%时,V_2O_5主要以结晶相存在,占据大量活性位,降低催化效果。由FWO法热力学分析得到颗粒氧化的活化能的顺序为EPM>EV5>EV10>EV40>EV20。

The Nano-scale V2O5/TiO2 catalysts for soot oxidation were prepared with different amount （5%, 10%, 20% and 40%） of V2O5 loaded on the TiO2 particles by an impregnation method. The structures and physico-chemical properties for those catalysts were characterized using Scanning electron microscope （SEM）, X-Ray diffraction （XRD） and Fourier transform infrared spectra （FT-IR）. Printex-U carbon black was chosen to replace the practical from soot engine. The catalytic activity for soot oxidation was evaluated using a TG/DTA analyzer. Based on Flynn-Wall-Ozawa method, the catalytic oxidation process of soot was quantitatively analyzed. The results show that when the V2O5 loading is low, the active vanadium oxygen species are in a high degree of dispersion, which basically present the state of monolayer distribution. When the V2O5 loading is 40%, part of the vanadium oxide species begin to reunite and appear obvious columnar crystal structure on the catalyst surface. With the increase of V2O5 loading, the catalytic activity of catalyst will increase, and the characteristic temperatures of soot oxidation will decrease. The catalyst loaded by V2O5 of 20% exhibits the highest catalytic activity for soot oxidation and the ignition temperature Ti, weightlessness peak temperature Tp and the burnout temperature Tf of soot oxidation present the biggest drop, as compared with the non-catalyzed particulates. When the V2O5 loading reaches 40%, the vanadium oxides mainly existing in the clusters of crystalline particles, occupy the active sites, which reduce the catalytic effect. The activation energy of soot oxidation calculated by FWO method can be arranged in descending order as follows ： EPM 〉 EVS〉 EV10 〉 EV40 〉 EV20.