塗佈二氧化鈦在二氧化矽及中孔洞材料作為五氧化二釩之擔體之氧化性觸媒研究; EXAFS and Catalytic Studies of V2O5 on TiO2 Grafted MCM-41 and SiO2

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題名:	塗佈二氧化鈦在二氧化矽及中孔洞材料作為五氧化二釩之擔體之氧化性觸媒研究;EXAFS and Catalytic Studies of V2O5 on TiO2 Grafted MCM-41 and SiO2
作者:	高聖倉;Sheng-Tsang Kao
貢獻者:	化學研究所
關鍵詞:	五氧化二釩;氧化;催化;中孔洞;二氧化鈦;catalyst;oxidation;EXAFS;XANES;V2O5;TiO2;mesoporous
日期:	2003-06-10
上傳時間:	2009-09-22 10:10:13 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本論文主要是以塗佈二氧化鈦在二氧化矽及中孔洞材料作為五氧化二釩之擔體所形成之釩觸媒之研究，利用鈦的前驅物Titanium isopropoxide中-(CH3CHOCH3)官能基與Si-OH反應的特性將鈦植接在SiO2及MCM-41上，經450℃高溫鍛燒後分別形成二氧化鈦擔體TiO2/SiO2及TiO2/MCM-41，而中孔洞之二氧化鈦擔體TiO2/MCM-41具有高於1200m2/g的表面積、26Å的孔洞大小及高達800℃的熱穩定性，再將釩的前驅物VO(OC3H7)3與二氧化鈦擔體反應，利用釩與鈦間較好的作用力及20wt%二氧化鈦在表面的高覆蓋度，將釩植接在二氧化鈦之上形成釩觸媒V2O5/TiO2/SiO2及V2O5/TiO2/MCM-41，並製作不含二氧化鈦的對照組V2O5/SiO2及V2O5/MCM-41，再以XANES、EXAFS、XRD、ASAP、ICP-MS及UV-Vis來分析其結構，而在含有二氧化鈦的釩觸媒中，其V-O-V較弱，即較少的釩形成聚合的VOx形態，而較傾向以獨立的VO4形態存在。利用釩觸媒做乙醇的選擇性氧化反應，結果顯示V2O5/TiO2/SiO2的轉化率約為80%，而V2O5/SiO2僅有20-30%，在選擇性方面V2O5/TiO2/SiO2也有較好的結果，另外利用物理的方式將V2O5/SiO2與TiO2/SiO2混合進行催化反應，結果顯示利用物理的混合雖然同時存在有五氧化二釩及二氧化鈦，但並不會提高反應的活性，僅為一相加的結果，無法達到V2O5/TiO2/SiO2的高活性及選擇性，而五氧化二釩在V2O5/TiO2/SiO2中以獨立的VO4形態存在及利用鈦(IV)較矽(IV)為低的陰電性，使得與釩之間的V-O-Ti鍵之間有較高的電子密度，而讓釩更利於行催化反應，才是達到高轉化率及選擇性的主因。 TiO2 grafted SiO2 and MCM-41 can be used as the TiO2 supports for V2O5 in order to provide a high surface TiO2 environment for the vanadium catalysts. Mesoporous TiO2/MCM-41 has a BET surface area of 1200m2/g with pore size 26 Å, and exhibits a thermal stable more than 800℃. The so prepared catalyst V2O5/TiO2/MCM-41 has a BET surface area of 700 m2/g with pore size 25Å. The presences of the strong pre-edge peak in the spectra of XANES of all vanadium catalysts suggest that vanadium atoms are located in a tetrahedral symmetry in all catalysts. Analysis of their EXAFS spectra revealed a peak appearing at 3.0 Å for V2O5/MCM-41 is mainly due to the presence of vanadium atoms adjacent to vanadium atoms (V-O-V). For V2O5/TiO2/MCM-41, relatively week V-O-V peak were observed in the Fourier transform of EXAFS. These indicate the vanadium oxide on MCM-41 and TiO2/MCM-41 were mostly in the form of polymers. A similar phenomenon was observed on V2O5/SiO2 as revealed by its EXAFS spectrum. However, for V2O5/TiO2/SiO2, almost no V-O-V peak were observed in the Fourier transform of EXAFS. This indicates that the vanadium oxide is mostly presented as isolated species. The higher reactive for TiO2 grafted sample may due to the well dispersion of vanadium species on the support. Oxidation of ethanol by air was carried on a fixed bath reactor. The catalyst V2O5/TiO2/SiO2 was found to have higher reactivity which may lie in the increase of the electron density of the bridging oxygen of the V-O-Support bond, since the Ti(IV) cations possess a lower electronegativity than the Si(IV) cations.
顯示於類別:	[化學研究所] 博碩士論文

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