Catalytic properties of Cr-containing heteropolytungstates in H2O2 participated reactions: H2O2 decomposition and oxidation of unsaturated hydrocarbons with H2O2
Catalytic properties of Cr-containing heteropolytungstates in H2O2 participated reactions: H2O2 decomposition and oxidation of unsaturated hydrocarbons with H2O2
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DOI：
10.1016/1381-1169(95)00291-x
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发表时间：
1996-05-25
影响因子：
--
通讯作者：
Likholobov, VA
中科院分区：
文献类型：
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作者：
Kuznetsova, NI;Kuznetsova, LI;Likholobov, VA
通过改变前驱体和反应步骤(升高温度、延长溶液放置时间、改变起始试剂的摩尔比和酸度)合成了含铬的PW11O397杂多阴离子衍生物(PW11Cr)，并用元素分析、UV-Vis和IR光谱对其进行了表征。考察了PW11Cr四丁基铵盐对H_2O_2分解和H_2O_2向烃类底物环己烯和苯的氧转移的催化作用。在所有其他合成条件相同的情况下，提高pH值可使样品的过氧化氢分解活性更高。在H_2O_2/PW11Cr体系中，苯生成苯酚，环己烯生成环己酮、环己醇和环氧环己烯的混合物。PW11Cr在碳氢化合物氧化反应中的活性受样品合成方法的影响。提出了不同的光谱特性和催化性能取决于铬(III)离子与PW11O397-阴离子之间的键性质。与典型的M取代多金属氧酸盐不同，所得到的样品中含有Cr(III)离子，这些离子可能与Keggin结构空位附近的PW11O397-杂多阴离子的表面氧原子有关。Cr(III)离子的表面位置有利于氧从H_2O_2向碳氢化合物转移。在H_2O_2存在下，W_(11)铬溶液与H_2O_2分解中间产物发生反应，可见吸收峰由15200~16300 cm(-1)移至15500~18000 cm(~(-1))。生成的氧化物种PW11Cr[O]是与不饱和碳氢化合物反应中的活性氧化剂。
Cr-containing derivatives of PW11O397- heteropolyanion (PW11Cr) were synthesized under variation of precursors and procedure (increasing temperature, prolonged keeping of solution, varying molar ratio of starting reagents and acidity) and characterized by elemental analysis, UV-Vis and IR spectroscopy. Tetrabutylammonium salts of PW11Cr were examined in catalysis of H2O2 decomposition and oxygen transfer from H2O2 to the hydrocarbon substrates, cyclohexene and benzene. With all the other conditions of synthesis identical, increasing the pH gave samples more active in H2O2 decomposition. In the H2O2/PW11Cr system, benzene formed phenol and cyclohexene formed a mixture of cyclohexenone, cyclohexenol and cyclohexene oxide. The activity of PW11Cr in hydrocarbon oxidation was sensitive to the procedure used for sample synthesis. Variable spectral characteristics and catalytic properties of PW11Cr samples were suggested to depend on the nature of bond between Cr(III) ion and PW11O397- anion. As distinguished from typical M-substituted polyoxometalates, the samples obtained contain Cr(III) ions which are probably connected with surface oxygen atoms of PW11O397- heteropolyanion near the vacancy of the Keggin structure. Surface location of Cr(III) ions is supposed to favor oxygen transfer from H2O2 to hydrocarbon. In the presence of H2O2, PW11Cr solutions showed the increase of visible absorption and a shift of its maximum from 15200-16300 to 15500-18000 cm(-1), that arose from the reaction of PW11Cr with intermediate products of the H2O2 decomposition. The resulting oxidized species PW11Cr[O] are active oxidants in the reaction with unsaturated hydrocarbons.