Carboxyl intermediate formation via an in situ-generated metastable active site during water-gas shift catalysis
Carboxyl intermediate formation via an in situ-generated metastable active site during water-gas shift catalysis
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DOI：
10.1038/s41929-019-0343-2
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发表时间：
2019-10-01
期刊：
影响因子：
37.8
通讯作者：
Szanyi, Janos
中科院分区：
文献类型：
--
作者：
Nelson, Nicholas C.;Manh-Thuong Nguyen;Szanyi, Janos
在低温水煤气变换反应过程中的催化途径和活性位点的连续实验证据仍然难以捉摸。在此，我们结合联合收割机光谱，动力学和计算分析，以解决几十年来的机制的争议，通过研究逆水煤气转移Pd/Al 2 O3。同位素瞬态动力学分析建立了甲酸中间体的次要作用，而氢滴定实验证实了羧基的中间性。能够解耦的平行的甲酸和羧基的途径导致一个独特的活性位点，表现出regioand化学选择性氢除了CO2产生的羧基中间体的识别。原位形成亚稳活性位点，导致金属-载体界面的羟基化和电子重组。活性中心电子结构和机械景观的原子模拟提供了一个与实验观察一致的框架。我们的研究强调了动态创建的一个coordinatively不饱和金属网站所造成的基板吸附在相邻的支持网站。
Definitive experimental proof for catalytic pathways and active sites during the low-temperature water-gas shift reaction remains elusive. Herein, we combine spectroscopic, kinetic and computational analyses to address the decades-long mechanistic controversy by studying the reverse water-gas shift over Pd/Al2O3. Isotopic transient kinetic analysis established the minor role of the formate intermediate, whereas hydrogen titration experiments confirmed the intermediacy of carboxyl. The ability to decouple the parallel formate and carboxyl pathways led to the identification of a distinct active site that exhibits regioand chemoselective hydrogen addition to CO2 to yield the carboxyl intermediate. The metastable active site is formed in situ, resulting in hydroxylation of the metal-support interface and electronic restructuring. Atomistic simulations of the active site electronic structure and mechanistic landscape provided a framework that is consistent with experimental observations. Our study highlights the dynamic creation of a coordinatively unsaturated metal site caused by substrate adsorption on an adjacent support site.