Controlled Synthesis, Characterization, and Catalytic Properties of Mn2O3 and Mn3O4 Nanoparticles Supported on Mesoporous Silica SBA-15

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• 作者：Yi-Fan Han ; Fengxi Chen ; Ziyi Zhong ; Kanaparthi Ramesh ; Luwei Chen ; Effendi Widjaja
• 刊名：Journal of Physical Chemistry B
• 出版年：2006
• 出版时间：December 7, 2006
• 年：2006
• 卷：110
• 期：48
• 页码：24450 - 24456
• 全文大小：301K
• 年卷期：v.110,no.48(December 7, 2006)
• ISSN：1520-5207

文摘

A method established in the present study has proven to be effective in the synthesis of Mn₂O₃ nanocrystalsby the thermolysis of manganese(III) acetyl acetonate ([CH₃COCH=C(O)CH₃]₃-Mn) and Mn₃O₄ nanocrystalsby the thermolysis of manganese(II) acetyl acetonate ([CH₃COCH=C(O)-CH₃]₂Mn) on a mesoporous silica,SBA-15. In particular, Mn₂O₃ nanocrystals are the first to be reported to be synthesized on SBA-15. Thestructure, texture, and electronic properties of nanocomposites were studied using various characterizationtechniques such as N₂ physisorption, X-ray diffraction (XRD), laser Raman spectroscopy (LRS), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy(XPS). The results of powder XRD at low angles show that the framework of SBA-15 remains unaffectedafter generation of the manganese oxide (MnO_x) nanoparticles, whereas the pore volume and the surface areaof SBA-15 dramatically decreased as indicated by N₂ adsorption-desorption. TEM images reveal that thepores of SBA-15 are progressively blocked with MnO_x nanoparticles. The formation of the hausmanniteMn₃O₄ and bixbyite Mn₂O₃ structures was clearly confirmed by XRD. The surface structures of MnO_x werealso determined by LRS, XPS, and TPR. The crystalline phases of MnO_x were identified by LRS withcorresponding out-of-plane bending and symmetric stretching vibrations of bridging oxygen species (M-O-M) of both MnO_x nanoparticles and bulk MnO_x. We also observed the terminal Mn=O bonds correspondingto vibrations at 940 and 974 cm^-1 for Mn₃O₄/SBA-15 and Mn₂O₃/SBA-15, respectively. These results showthat the MnO_x species to be highly dispersed inside the channels of SBA-15. The nanostructure of the particleswas further identified by the TPR profiles. Furthermore, the chemical states of the surface manganese (Mn)determined by XPS agreed well with the findings of LRS and XRD. These results suggest that the methoddeveloped in the present study resulted in the production of MnO_x nanoparticles on mesoporous silica SBA-15 by controlling the crystalline phases precisely. The thus-prepared nanocomposites of MnO_x showedsignificant catalytic activity toward CO oxidation below 523 K. In particular, the MnO_x prepared frommanganese acetyl acetonate showed a higher catalytic reactivity than that prepared from Mn(NO₃)₂.