| dc.description.abstract | In this research, a series of Ce1-xMnxO2 mixed oxide supports with different compositions were prepared by co-precipitation method for enhancing the redox properties of the CeO2. Ag/Ce1-xMnxO2 catalysts were prepared by impregnation method and their performance in the oxidation of volatile organic compound benzene was evaluated. In addition to the effect of calcination temperature, the ratio of Ce/Mn, the incorporation of Zr and Ag loading were investigated, the roles of Ce1-xMnxO2 mixed oxides and Ag were also discussed. The benzene vapor feed was diluted with air into the reactor at the flow rate of 100 ml/min (F/W = 6000~24000 ml h-1gcat-1). The physical and surface properties of the prepared catalysts were characterized by BET, XRD, Raman, H2-TPR and XPS.
Incorporating maganese into CeO2 increased the specific surface area of supports. Part of manganese species which entered into the ceria lattice to form Ce1-xMnxO2 solid solutions improved the redox properties, and the increase of Mn3+ and defect oxygen were caused by the part of MnOx dispersed on the surface of Ce1-xMnxO2. The aggregation of MnOx on surface occurred when the fraction of Mn in Ce1-xMnxO2 exceeded 0.5. The specific surface area and redox properties of supports could be enhanced through the incorporation of Zr into Ce1-xMnxO2 to form Ce0.9-xZr0.1MnxO2.
The reactivities of the Ag catalysts supported on Ce1-xMnxO2 were higher than those supported on CeO2 and MnOx catalysts. The best performance in total oxidation of bezene was 7%Ag/Ce0.6Mn0.4O2 catalyst (T100 = 185 °C). It had no promoting effect on Ag/Ce0.9-xZr0.1MnxO2 catalysts with the introduction of Zr.
The Ag catalysts supported on SiO2 and γ-Al2O3 supports without redox properties showed good activity for benzene oxidation. There were two oxidation states of silver, Ag0 and Ag+, on the surface of catalyst. The dominant species of silver was Ag0, but Ag+ was the more active of the two. The activity of Ag/CeO2 catalyst was higher than Ag/SiO2, therefore, the redox properties of supports that enhanced the catalytic activity were necessary. The redox properties of Ce0.9-xZr0.1MnxO2 were more than that of Ce1-xMnxO2, and the catalytic activity of former was also better than that of latter over benzene oxidation. However, the reactivity of Ag/Ce0.9-xZr0.1MnxO2 was equivalent to that of Ag/Ce1-xMnxO2. Ag was an important active species for total oxidation of benzene, and the part of the maganese that was in the form of well dispersed phase of MnOx also played a key role of catalytic oxidation of benzene. Nevertheless, the degree of redox behavior of supports was not a key to the reactivities.
Oxidation of benzene over Ag/Ce1-xMnxO2 was along four paths. Benzene that had been adsorbed on Ce1-xMnxO2 was oxidized by the release of oxygen from Ce1-xMnxO2. The benzene could be adsorbed on Ag and oxidized by oxygen that was released from Ce1-xMnxO2. The benzene could be adsorbed on Ag2O as well, and oxidized by oxygen that was released from Ag2O. Moreover, oxygen was also adsorbed on Ag and then reacted with adsorbed benzene.
Ag/Ce1-xMnxO2 catalysts whose catalytic performance in the oxidation of benzene were better than based metal CuO and noble metal Pd catalysts exhibited high reaction stability in the suitable condition, and that could eliminate a wide range of concentration of benzene. It is a very ideal and practical catalyst for complete oxidation of benzene.
| en_US |