On the Utility of Ce 3+ Spin−Orbit Transitions in the Interpretation of Rate Data in Ceria Catalysis: Theory, Validation, and Application
On the Utility of Ce 3+ Spin−Orbit Transitions in the Interpretation of Rate Data in Ceria Catalysis: Theory, Validation, and Application
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关于 Ce 3 自旋轨道跃迁在解释二氧化铈催化速率数据中的效用：理论、验证和应用
DOI：
10.1021/acs.jpcc.2c06637
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发表时间：
2023
期刊：
影响因子：
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通讯作者：
Bollini, Praveen
中科院分区：
文献类型：
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作者：
Afrin, Sadia;Bollini, Praveen
氧化铈是工业和学术界感兴趣的催化系统中普遍存在的成分，而氧空位/Ce3+离子的精确机械功能是这方面持续存在的悬而未决的问题。现有的量化空位密度的方法在本质上大部分是间接的，并且它们要么必须在异位应用，要么如果在原位适用，则通常在适用性或定量严格性方面受到限制。我们在此提出了 2F5/2–2F7/2 电子跃迁在氧空位或 Ce3+ 密度定量估计中的实用性的理论和实验分析。晶体场理论的应用揭示了C3v位点对称环境中存在的Ce3+离子的2F5/2–2F7/2跃迁的非禁禁性质，这与气相中的游离Ce3+离子在等效宇称状态之间表现出La Porte禁禁跃迁不同。使用三种还原剂（H2、CO 和乙醇）估算感兴趣的红外特征的摩尔消光系数，并将其应用于二氧化铈催化的 H2-D2 交换和叔丁醇脱水催化速率数据的解释。 H2-D2交换率与红外光谱衍生的空位密度之间的线性相关性表明，还原域仅参与氢化和加氢脱氧催化中普遍存在的H2活化步骤。相比之下，在存在和不存在具有化学计量氧化途径倾向的α-含氢含氧化合物的情况下，正叔丁醇脱水速率与空位密度成反比，这表明在产生异丁烯的脱水转化中氧化域而不是还原域参与。 Ce3+2F5/2–2F7/2转变的非禁止性质（此处使用对称性考虑得到证明）可能超出此处考虑的C3v对称环境，这意味着它在电磁波谱红外区域内的偶然出现可能使其适合于更广泛地将局部结构与二氧化铈催化中的催化功能相关联的定量应用。
Cerium oxide is a ubiquitous component in catalytic systems of industrial and academic interest, and the precise mechanistic function of oxygen vacancies/Ce3+ions a persistent open question in this regard. Existing methods for quantifying vacancy densities are for the most part indirect in nature, and they either have to necessarily be applied ex situ or, if applicable in situ, are oftentimes limited in applicability or quantitative rigor. We present herein a theoretical and experimental analysis of the utility of2F5/2–2F7/2electronic transitions in the quantitative estimation of oxygen vacancy or Ce3+densities. Application of crystal field theory reveals the nonforbidden nature of2F5/2–2F7/2transitions for Ce3+ions present in aC3vsite symmetry environment, unlike free Ce3+ions in the gas phase that exhibit La Porte forbidden transitions between states of equivalent parity. The molar extinction coefficient for the infrared feature of interest is estimated using three reductants─H2, CO, and ethanol─and applied toward interpretation of ceria-catalyzed H2–D2exchange andtert-butanol dehydration catalysis rate data. Linear correlations between H2–D2exchange rates and infrared spectroscopy-derived vacancy densities point to the sole involvement of reduced domains in H2activation steps prevalent in hydrogenation and hydrodeoxygenation catalysis. Contrastingly, arealtert-butanol dehydration rates that trend inversely with vacancy densities both in the presence and absence of α-hydrogen-containing oxygenates carrying a propensity toward stoichiometric oxidative routes suggest the participation of oxidized, not reduced domains in dehydrative turnovers producing isobutene. The nonforbidden nature of the Ce3+2F5/2–2F7/2transition─evidenced here using symmetry considerations─likely extends beyond theC3vsymmetry environment under consideration here, implying that its fortuitous appearance within the infrared region of the electromagnetic spectrum may render it amenable to quantitative application in relating local structure to catalytic function in ceria catalysis more broadly.