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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Decamolybdocobaltate heteropolyanions in aqueous solutions: Chemistry driving their formation and domains of stability
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Decamolybdocobaltate heteropolyanions in aqueous solutions: Chemistry driving their formation and domains of stability

机译：水溶液中的十钼酸双杂十二酸杂多阴离子：化学作用驱动其形成和稳定性域

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In the present study, aqueous solutions of decamolybdocobaltate H _4Co _2Mo _(10)O _(38) ~6- heteropolyanions were prepared from molybdenum oxide, cobalt carbonate precursors and hydrogen peroxide used as oxidizing agent. The preparation was optimized adding a consecutive hydrothermal treatment at 150 °C to obtain pure H _4Co _2Mo _(10)O _(38) ~6- aqueous solutions for Co/Mo atomic ratio of 0.5. Combining quantitative Raman and UV-visible measurements and chemometric methods, it was demonstrated that a mixture of H _4Co _2Mo _(10)O _(38) ~6- and octomolybdate Mo _8O _(26) ~4- species is obtained for Co/Mo ratios lower than 0.5, and the relative quantities of H _4Co _2Mo _(10)O _(38) ~6- are determined by the presence of Mo _8O _(26) ~4- species and by the quantity of Co ~(2+) countercations available in the solutions to ensure the electroneutrality. As these quantities can be predicted for each Co/Mo ratio, this finding allows rationalization of the preparation of heterogeneous catalysts using impregnation by H _4Co _2Mo _(10)O _(38) ~6- aqueous solutions. Parameters relevant of the impregnation step such as the pH, the Co/Mo ratio, and the molybdenum concentration were varied to determine the domains of stability of H _4Co _2Mo _(10)O _(38) ~6- heteropolyanions after formation. Stable from pH 1 to 4.5, this dimeric Anderson species is destabilized above pH 4.5; Co ~(2+), monomolybdate MoO _4 ~2- ions, and precipitates are then formed. For Co/Mo ratios lower than 0.5, the relative quantity of dimer does not vary with the pH and with a change of the Co/Mo ratio consecutive to the hydrothermal treatment. On the contrary, the coproduced Mo _8O _(26) ~4- species can be transformed into other isopolymolybdates varying the pH according to their domains of stability. For all of the ratios, H _4Co _2Mo _(10)O _(38) ~6- dimers were also shown to be stable in a wide range of molybdenum concentrations
机译：本研究以氧化钼，碳酸钴前驱体和过氧化氢为氧化剂，制备了十钼酸双钼酸H_4Co_2Mo_（10）O_（38）〜6-杂多阴离子水溶液。优化制备方法，并在150°C下进行连续水热处理，以获得Co / Mo原子比为0.5的纯H _4Co _2Mo _（10）O _（38）〜6-水溶液。结合定量拉曼光谱和紫外可见测量以及化学计量学方法，结果表明，对于Co，可以获得H _4Co _2Mo _（10）O _（38）〜6-和八钼酸盐Mo _8O _（26）〜4-的混合物/ Mo比值低于0.5，H _4Co _2Mo _（10）O _（38）〜6-的相对量由Mo _8O _（26）〜4-种类的存在和Co〜的量决定溶液中有（2+）个抗衡阳离子，可确保电子中性。由于可以针对每个Co / Mo比预测这些数量，因此，该发现可以合理地使用H _4Co _2Mo _（10）O _（38）〜6-水溶液浸渍来制备非均相催化剂。改变与浸渍步骤有关的参数，例如pH，Co / Mo比和钼浓度，以确定形成后H _4Co _2Mo _（10）O _（38）〜6-杂多阴离子的稳定性域。此二聚体安德森物质在pH 1至4.5稳定，在pH 4.5以上不稳定。 Co〜（2+），单钼酸盐MoO_4〜2-离子，然后形成沉淀。对于低于0.5的Co / Mo比，二聚体的相对量不随pH值变化并且在水热处理之后不随Co / Mo比的变化而变化。相反，根据其稳定性域，可以将共同产生的Mo _8O _（26）〜4-物种转化为其他改变pH的异多钼酸盐。对于所有比率，H _4Co _2Mo _（10）O _（38）〜6-二聚体也显示在宽范围的钼浓度下稳定

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