Coverage-Dependent Rate-Driving Force Relationships: Hydrogen Transfer from Cerium Oxide Nanoparticle Colloids
Coverage-Dependent Rate-Driving Force Relationships: Hydrogen Transfer from Cerium Oxide Nanoparticle Colloids
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覆盖度相关的速率-驱动力关系：纳米CeO_2胶体中的氢转移
DOI：
10.1021/jacs.2c07988
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发表时间：
2022-11-02
影响因子：
15
通讯作者：
Mayer, James M.
中科院分区：
文献类型：
--
作者：
Agarwal, Rishi G.;Mayer, James M.
速率-驱动力关系，称为Bronsted-Evans-Polanyi（BEP）关系，是许多用于预测多相催化剂和电催化剂性能的方法的核心。塔菲尔图和“火山”分析等方法通常假设吸附物覆盖度对不同材料反应速率的影响是恒定的和已知的。在这里，我们使用紫外-可见光谱测试这些假设，通过测量净氢原子转移率从胶体氧化铈纳米粒子（nanoceria）的有机试剂在不同的表面CeO-H键强度和表面覆盖率。所得速率常数遵循线性BEP关系，Δ log（k）= α Δ log（K-eq），跨越两种尺寸的纳米氧化铈、两种有机试剂和类似于10 kcal mol（-1）范围的CeO-H键强度。有趣的是，布朗斯台德斜率仅为0.2，表明速率常数对CeO-H键强度的敏感性远远低于通常假设的异质纳米材料。此外，当通过有机试剂键强度而不是CeO-H键强度改变反应驱动力时，我们观察到Bronsted斜率>1。这些布朗斯台德斜率协调或逐步机制的影响进行了讨论。据我们所知，这是第一个解决方案相测量的BEP关系的氢覆盖（纳米）材料。
Rate-driving force relationships, known as Bronsted-Evans-Polanyi (BEP) relations, are central to many methods for predicting the performance of heterogeneous catalysts and electrocatalysts. Methods such as Tafel plots and "volcano" analyses often assume that the effect of adsorbate coverage on reaction rates across different materials is constant and known. Here, we use UV-visible spectroscopy to test these assumptions by measuring rates of net hydrogen atom transfer from colloidal cerium oxide nanoparticles (nanoceria) to organic reagents at varying surface CeO-H bond strengths and surface coverages. The resulting rate constants follow a linear BEP relationship, Delta log(k) = alpha Delta log(K-eq), across two sizes of nanoceria, two organic reagents, and a similar to 10 kcal mol(-1) range of CeO-H bond strengths. Interestingly, the Bronsted slope is only 0.2, demonstrating that the rate constants are far less sensitive to CeO-H bond strength than would commonly be assumed for a heterogeneous nanomaterial. Furthermore, we observe a Bronsted slope >1 when altering the reaction driving force via the organic reagent bond strength instead of that of CeO-H. The implications of these Bronsted slopes for either concerted or stepwise mechanisms are discussed. To our knowledge, these are the first solution-phase measurements of BEP relationships for hydrogen coverage on a (nano)material.