Grafting of vanadyl acetylacetonate onto organo-hexagonal mesoporous silica and catalytic activity in the allylic epoxidation of geraniol
Grafting of vanadyl acetylacetonate onto organo-hexagonal mesoporous silica and catalytic activity in the allylic epoxidation of geraniol
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DOI：
10.1016/j.poly.2008.12.049
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发表时间：
2009-04
期刊：
影响因子：
2.6
通讯作者：
Bruno Jarrais;C. Pereira;Ana L. R. Silva;A. Carvalho;J. Pires;C. Freire
中科院分区：
文献类型：
--
作者：
Bruno Jarrais;C. Pereira;Ana L. R. Silva;A. Carvalho;J. Pires;C. Freire
乙酰丙酮氧钒采用三种不同的方法将（[VO（acac）2]）接枝到六方介孔二氧化硅（HMS）上：方法A -直接络合物固定化;方法B -用3-氨丙基三乙氧基硅烷（APTES）官能化HMS，然后络合物固定化;和方法C -用三甲基乙氧基硅烷（TMS）处理通过方法B制备的APTES官能化载体以使最终未反应的表面硅烷醇基团失活，随后进行络合物接枝。所有材料均通过氮元素分析、XPS、FTIR、-196 °C下的N2吸附等温线表征，并且[VO（acac）2]基材料还通过钒ICP-AES分析表征。结果表明，在方法B中，APTES成功地接枝到HMS上，接枝效率为90%，[VO（acac）2]复合物主要共价连接在HMS的内孔中，接枝效率为65%.在方法C中，获得较低的复合物固定效率，c.a. 25%，但复合物在整个官能化材料中共价键合。在方法A的情况下，母体HMS材料固定了非常少量的钒络合物（效率的2%），主要通过非共价相互作用固定在外表面中。以叔丁基过氧化氢（t-BuOOH）为氧源，考察了[VO（acac）2]基材料在香叶醇环氧化反应中的催化活性。在非均相反应中形成的两种环氧化物的选择性与在均相中观察到的那些相似，并且主要反应产物总是2，3-环氧香叶醇。通过方法B获得了允许较高底物转化率的催化剂，但是当考虑活性相的浸出时，方法C产生了最有效的催化剂。
Vanadyl(IV) acetylacetonate ([VO(acac)2]) was grafted onto a hexagonal mesoporous silica (HMS) using three different methodologies: method A – direct complex immobilisation; method B – functionalisation of the HMS with 3-aminopropyltriethoxysilane (APTES) followed by the complex immobilisation; and method C – treatment of the APTES functionalised support prepared by method B with trimethylethoxysilane (TMS) to deactivate eventually unreacted surface silanol groups, followed by complex grafting. All the materials were characterised by nitrogen elemental analysis, XPS, FTIR, N2adsorption isotherms at −196°C and the [VO(acac)2] based materials were also characterised by vanadium ICP-AES analysis. The results indicated that, in method B, APTES was successfully grafted onto the HMS with 90% of efficiency and allowed the covalent attachment of [VO(acac)2] complex mainly in the inner pores with an efficiency of 65%. In method C, a lower complex immobilisation efficiency was obtained, c.a. 25%, but the complex was covalently bonded throughout the functionalised material. In the case of method A, the parent HMS material immobilised a very low quantity of vanadium complex (2% of efficiency), mainly in the external surface through non-covalent interactions. The catalytic activity of [VO(acac)2] based materials in the epoxidation of geraniol using tert-butyl hydroperoxide (t-BuOOH) as oxygen source was assessed. The selectivities of the two epoxides formed in the heterogeneous phase reactions were similar to those observed in the homogeneous phase and the major reaction product was always 2,3-epoxygeraniol. The catalyst which allowed higher substrate conversion was obtained by method B but, when considering the leaching of the active phase, method C produced the most efficient catalyst.