Surface-Assisted Keto-Enol Tautomerism as a First Step in Heterogeneously Catalyzed Hydrogenation of Carbonyl Compounds

表面辅助酮-烯醇互变异构作为羰基化合物多相催化氢化的第一步

• 批准号: 457707951
• 负责人: Professorin Dr. Swetlana Schauermann
• 金额: --
• 依托单位: Institut für Physikalische Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/457707951?language=en
• 关键词: Surface; Assisted; Keto; Enol; Tautomerism

Heterogeneously catalysed hydrogenation of carbonyl compounds is a key step for many technically relevant processes. It relies on the activation of a highly stable C=O bond, which is difficult to achieve. Recently, an alternative low-barrier hydrogenation pathway of carbonyl compounds was predicted theoretically, which is based on a two-step process: (1) keto-enol tautomerisation of carbonyl species to the enol form followed by (2) H insertion into the newly formed C=C bond of enol. In these studies, both reaction steps exhibit significantly lower activation barriers as compared to the direct H insertion into the original stable carbonyl bond. This alternative mechanism opens up a prospect of a low-barrier pathway for hydrogenation of simple carbonyls relying on keto-enol tautomerisation as the first reaction step. Recently, we obtained the first experimental confirmation of the predicted reaction route. We also demonstrated that H insertion occurs not in an enol monomer as predicted theoretically, but in enol-ketone dimers, in which normally less stable enol species is stabilized via hydrogen bonding between the –OH group of the enol and the carbonyl group of a neighbouring molecule. External stabilization of enol species by foreign carbonyl-containing adsorbates was identified as a crucial step in enol-mediated low-barrier hydrogenation. This observation opens up a prospect of controlling this process via functionalization of the catalytic surface with stable foreign modifier molecules capable of enol stabilization and activation. The microscopic-level understanding of the underlying surface processes, however, is still largely missing.With the proposed research we are aiming at an atomistic-level understanding of enol-mediated heterogeneous hydrogenation catalysis occurring at metal surfaces, both pristine and functionalized with modifier species, that are capable of enol stabilization and activation. The focus of this study will be on exploring the mechanisms of keto-enol tautomerisation, enol stabilization and enol-mediated hydrogenation for different classes of carbonyl compounds; spectroscopic and microscopic identification of surface species formed under the reaction conditions; monitoring their dynamic changes and correlating this structural information with the reaction kinetics obtained under controlled isothermal conditions by molecular beam techniques.We will apply a unique combination of surface-sensitive techniques on well-defined model catalysts – both metal single crystals and metallic nanoparticles supported on model oxides, pristine and functionalized – to explore the fundamentals of enol-mediated hydrogenation of carbonyl compounds and obtain detailed structure-reactivity relationships. The outcome of this research holds a great potential for developing new concepts towards rational-based design of surfaces with tailor-made catalytic properties.

羰基化合物的非均相催化加氢是许多技术相关工艺的关键步骤。它依赖于高度稳定的C=O键的活化，这是很难实现的。最近，理论上预测了羰基化合物的另一种低势垒氢化途径，该途径基于两步过程：（1）羰基物种的酮-烯醇互变异构为烯醇形式，然后（2）H插入到烯醇新形成的C=C键中。在这些研究中，这两个反应步骤表现出显着较低的活化势垒相比，直接H插入到原来的稳定的羰基键。这种替代机制开辟了一个前景的低障碍途径氢化简单的羰基依赖于酮-烯醇互变异构作为第一个反应步骤。最近，我们获得了预测的反应路线的第一个实验确认。我们还表明，H插入发生在烯醇单体的理论预测，但在烯醇-酮二聚体，其中通常不太稳定的烯醇物种是通过稳定的-OH基团的烯醇和相邻分子的羰基之间的氢键。在烯醇介导的低阻氢化反应中，含羰基的吸附物对烯醇物种的外部稳定是一个关键步骤。这一观察结果开辟了一个前景控制这一过程，通过功能化的催化表面与稳定的外来改性剂分子能够烯醇稳定和活化。微观层面的理解的基础表面过程，但是，仍然在很大程度上missing.With拟议的研究，我们的目标是在原子级的理解烯醇介导的多相加氢催化发生在金属表面，无论是原始的和功能化的改性剂物种，这是能够烯醇稳定和活化。本研究的重点是探索不同类型羰基化合物的酮-烯醇互变异构、烯醇稳定化和烯醇介导的氢化反应机理，以及在反应条件下形成的表面物种的光谱和显微鉴定;监测它们的动态变化，并将这些结构信息与通过分子束技术在受控等温条件下获得的反应动力学相关联。在明确定义的模型催化剂上的表面敏感技术的独特组合-支持在模型氧化物上的金属单晶和金属纳米颗粒，原始的和官能化的-探索烯醇介导的羰基化合物氢化的基本原理，并获得详细的结构-反应性关系。这项研究的结果具有很大的潜力，为开发新的概念，以合理的设计与定制的催化性能的表面。