Clarification and control of the active sites at the atomic/molecular level are important to develop nanocatalysts. The catalytic performance of two oxidation states of nitrate-incorporating octadecavanadates, [V₁₈O₄₆(NO₃)]⁵⁻ (V18) and [V₁₈O₄₆(NO₃)]⁴⁻ (V18ox), and a copper-substituted one, [Cu₂V₁₆O₄₄(NO₃)]⁵⁻ (Cu2V16), in selective oxidation was investigated. Both V18 and V18ox possessed the same double-helical structures and one of two tetravalent vanadium sites of V18 was oxidized in V18ox. The comparison of the mobility of the incorporated nitrate reveals that tetravalent vanadium centres show stronger interaction with the incorporated anions than pentavalent ones. The oxidation reaction with V18ox proceeded more smoothly with tert-BuOOH as an oxidant than that with V18. The reactivity and selectivity of the oxidation of 2-cyclohexen-1-ol were different among the derivatives. V18ox showed the higher reactivity with 72% selectivity to epoxide. With V18, reactivity was lower but higher selectivity to epoxide was achieved. In the presence of Cu2V16, 2-cyclohexen-1-one was selectively obtained with 81% selectivity. The order of the reactivity for cyclooctene was V18ox, V18 and Cu2V16. These results shows that the cap part of the double-helix acts as the active site. Even though the vanadium–oxygen species exhibit the same structures, the catalytic properties can be controlled by changing the valence of vanadium and metal substitution.

中文翻译：

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通过改变氧化态和金属取代来控制掺入硝酸盐的十八烷酸盐的反应性

在原子/分子水平上澄清和控制活性位点对于开发纳米​​催化剂非常重要。硝酸根十八烷酸盐的两种氧化态[V ₁₈ O ₄₆ (NO ₃ )] ⁵⁻ (V18)和[V ₁₈ O ₄₆ (NO ₃ )] ⁴⁻ (V18ox)和铜取代的催化性能研究了一种[Cu ₂ V ₁₆ O ₄₄ (NO ₃ )] ⁵⁻ (Cu2V16) 在选择性氧化中的作用。 V18和V18ox都具有相同的双螺旋结构，并且V18的两个四价钒位点之一在V18ox中被氧化。掺入硝酸盐迁移率的比较表明，四价钒中心与掺入阴离子的相互作用比五价钒中心更强。以叔BuOOH为氧化剂，V18ox的氧化反应比V18的氧化反应进行得更顺利。 2-环己烯-1-醇的氧化反应活性和选择性在衍生物之间有所不同。 V18ox 显示出较高的反应活性，对环氧化物的选择性为 72%。使用 V18，反应活性较低，但对环氧化物的选择性较高。在Cu2V16存在下，选择性地得到2-环己烯-1-酮，选择性为81%。环辛烯的反应活性顺序为V18ox、V18和Cu2V16。这些结果表明双螺旋的帽部分充当活性位点。尽管钒-氧物质表现出相同的结构，但可以通过改变钒和金属取代的价态来控制催化性能。