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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Cerium Oxyhydroxide Clusters: Formation, Structure, and Reactivity
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Cerium Oxyhydroxide Clusters: Formation, Structure, and Reactivity

机译：羟基氧化铈团簇：形成，结构和反应活性

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摘要

Cerium oxyhydroxide cluster anions were produced by irradiating ceric oxide particles by using 355 nm laser pulses that were synchronized with pulses of nitrogen gas admitted to the irradiation chamber. The gas pulse stabilized the nascent clusters that are largely anhydrous [Ce_xO_y] ions and neutrals. These initially formed species react with water, principally forming oxohydroxy species that are described by the general formula [Ce_xO_y(OH)_z]- for which all the Ce atoms are in the IV oxidation state. In general, the extent of hydroxylation varies from a value of three OH per Ce atom when x = 1 to a value slightly greater than 1 for x a 8. The Ce_3 and Ce_6 species deviate significantly from this trend: the x = 3 cluster accommodates more hydroxyl moieties compared to neighboring congeners at x = 2 and 4. Conversely, the x = 6 cluster is significantly less hydroxylated than its x = 5 and 7 neighbors. Density functional theory (DFT) modeling of the cluster structures shows that the hydrated clusters are hydrolyzed, and contain one-to-multiple hydroxide moieties, but not datively bound water. DFT also predicts an energetic preference for formation of highly symmetric structures as the size of the clusters increases. The calculated structures indicate that the ability of the Ce_3 oxyhydroxide to accommodate more extensive hydroxylation is due to a more open, hexagonal structure in which the Ce atoms can participate in multiple hydrolysis reactions. Conversely the Ce_6 oxyhydroxide has an octahedral structure that is not conducive to hydrolysis. In addition to the fully oxidized (Ce(IV)) oxyhydroxides, reduced oxyhydroxides (containing a Ce(III) center) are also formed. These become more prominent as the size of the clusters increases, suggesting that the larger cena clusters have an increased ability to accommodate a reduced Ce(III) moiety. In addition, the spectra offer evidence for the formation of superoxide derivatives that may arise from reaction of the reduced oxyhydroxides with dioxygen. The overall intensity of the clusters tends to monotonically decrease as the cluster size increases; however, this trend is interrupted at Ce_(13), which is significantly more stable compared to neighboring congeners, suggesting formation of a dehydrated Keggin_type structure.
机译：通过使用355nm的激光脉冲辐照二氧化铈颗粒来产生羟基氧化铈簇阴离子，所述355nm激光脉冲与进入辐照室的氮气脉冲同步。气体脉冲稳定了主要是无水[Ce_xO_y]离子和中性粒子的新生簇。这些最初形成的物质与水反应，主要形成由通式[Ce_xO_y（OH）_z]-所描述的氧代羟基物质，其所有Ce原子均处于IV氧化态。通常，羟基化的程度从x = 1时每个Ce原子的三个OH值到xa 8的值略大于1的值而变化。Ce_3和Ce_6物种明显偏离此趋势：x = 3团簇可容纳更多与在x = 2和4时相邻的同类物相比，羟基部分。相反，x = 6簇的羟基化程度明显低于其x = 5和7个邻居。团簇结构的密度泛函理论（DFT）建模表明，水合团簇被水解，并且包含一个至多个氢氧化物部分，但没有键结水。 DFT还预测随着簇的大小增加，强烈倾向于形成高度对称的结构。计算的结构表明，Ce_3羟基氢氧化物适应更广泛的羟基化的能力归因于更开放的六角形结构，其中Ce原子可以参与多个水解反应。相反，Ce_6羟基氧化物具有不利于水解的八面体结构。除完全氧化的（Ce（IV））羟基氧化物外，还形成还原的羟基氧化物（含Ce（III）中心）。随着簇的大小增加，这些变得更加突出，表明较大的塞纳簇具有增加的能力以适应减少的Ce（III）部分。另外，光谱提供了由还原的羟基氧化物与双氧反应产生的超氧化物衍生物形成的证据。簇的总体强度随着簇大小的增加而趋于单调降低。但是，这种趋势在Ce_（13）处被中断，与相邻同类物相比，Ce_（13）明显更稳定，表明形成了脱水的Keggin_type结构。

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