Highly dispersed ruthenium hydroxide supported on titanium oxide effective for liquid-phase hydrogen-transfer reactions.
Highly dispersed ruthenium hydroxide supported on titanium oxide effective for liquid-phase hydrogen-transfer reactions.
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DOI：
10.1002/chem.200801655
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发表时间：
2008-12
期刊：
影响因子：
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通讯作者：
K. Yamaguchi;T. Koike;J. Kim;Y. Ogasawara;N. Mizuno
中科院分区：
文献类型：
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作者：
K. Yamaguchi;T. Koike;J. Kim;Y. Ogasawara;N. Mizuno
负载型氢氧化钌催化剂(Ru（OH)(x)/载体）采用三种不同的TiO(2)载体(锐钛矿TiO(2)(A)， BET表面积：316 m(2) g(-1))，锐钛矿TiO(2)(TiO(2)(B), 73 m(2) g(-1))，金红石TiO(2)(TiO(2)(C), 3.2 m(2) g(-1)))，以及Al(2)O(3)载体(160 m（2) g(-1)）制备。利用x射线衍射（XRD）、x射线光电子能谱（XPS）、电子自旋共振（ESR）和x射线吸收精细结构（XAFS）对产物进行表征，发现存在单体氢氧化钌和聚合氢氧化钌。从最近邻Ru原子的配位数和ESR信号的强度来看，单体氢氧化物种类的增加顺序为Ru(OH)(x)<Ru(OH)(x)/TiO(2)(C)<Ru(OH)(x)/Al(2)O(3)<Ru(OH)(x)/TiO(2)(B)<Ru(OH)(x)/TiO(2)(A)。这些负载型氢氧化钌催化剂，特别是Ru(OH)(x)/TiO(2)(A)，对手性仲醇的外消旋、羰基化合物和烯丙醇的还原等液相氢转移反应表现出较高的催化活性和选择性。Ru(OH)(x)/TiO(2)(A)对这些氢转移反应的催化活性比以前报道的异相催化剂(如Ru(OH)(x)/Al（2)O(3)）的催化活性至少高一个数量级。这些催化剂是真正的多相催化剂，反应后回收的催化剂可以多次重复使用而不损失催化性能。随着氢氧化钌单体种类的增加，反应速率单调增加，表明氢氧化钌单体种类对这些氢转移反应是有效的。
Supported ruthenium hydroxide catalysts (Ru(OH)(x)/support) were prepared with three different TiO(2) supports (anatase TiO(2) (TiO(2)(A), BET surface area: 316 m(2) g(-1)), anatase TiO(2) (TiO(2)(B), 73 m(2) g(-1)), and rutile TiO(2) (TiO(2)(C), 3.2 m(2) g(-1))), as well as an Al(2)O(3) support (160 m(2) g(-1)). Characterizations with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and X-ray absorption fine structure (XAFS) showed the presence of monomeric ruthenium(III) hydroxide and polymeric ruthenium(III) hydroxide species. Judging from the coordination numbers of the nearest-neighbor Ru atoms and the intensities of the ESR signals, the amount of monomeric hydroxide species increased in the order of Ru(OH)(x)<Ru(OH)(x)/TiO(2)(C)<Ru(OH)(x)/Al(2)O(3)<Ru(OH)(x)/TiO(2)(B)<Ru(OH)(x)/TiO(2)(A). These supported ruthenium hydroxide catalysts, especially Ru(OH)(x)/TiO(2)(A), showed high catalytic activities and selectivities for liquid-phase hydrogen-transfer reactions, such as racemization of chiral secondary alcohols and the reduction of carbonyl compounds and allylic alcohols. The catalytic activities of Ru(OH)(x)/TiO(2)(A) for these hydrogen-transfer reactions were at least one order of magnitude higher than those of previously reported heterogeneous catalysts, such as Ru(OH)(x)/Al(2)O(3). These catalyses were truly heterogeneous, and the catalysts recovered after the reactions could be reused several times without loss of catalytic performance. The reaction rates monotonically increased with an increase in the amount of monomeric ruthenium hydroxide species, which suggests that the monomeric species are effective for these hydrogen-transfer reactions.