Das Amitabha, Mandal Shyama Charan, Pathak Biswarup
Department of Chemistry, Indian Institute of Technology Indore, Indore 453552, India.
Phys Chem Chem Phys. 2022 Apr 6;24(14):8387-8397. doi: 10.1039/d1cp05144j.
The conversion of CO to DMM is an important transformation for various reasons. Co and Ru-based triphos catalysts have been investigated using density functional theory (DFT) calculations to understand the mechanistic pathways of the CO to DMM conversion and the role of noble/non-noble metal-based catalysts. The reaction has been investigated sequentially through methylformate (MF) and methoxymethane (MM) intermediates as they are found to be important intermediates. For the hydrogenation of CO and MF, the hydrogen sources such as H and methanol have been investigated. The calculated reaction free energy barriers for all the possible pathways suggest that both hydrogen sources are important for the Co-triphos catalyst. However, in the case of the Ru-triphos catalyst, molecular H is calculated to be the only hydrogen source. Various esterification and acetalization possibilities have also been explored to find the most favorable pathway for the conversion of CO to DMM. We find that the hydride transfer to the CO is the rate determining step (RDS) for the overall reaction. Our mechanistic investigation reveals that the metal center is the active part for the catalysis rather than the Brønsted acid and the redox triphos ligand plays an important role through the push-pull mechanism. The implemented microkinetic study shows that the reaction is also quite dependent on the concentration of the gaseous reactants and the rate constant increases exponentially above 363 K.
出于多种原因，一氧化碳（CO）转化为二甲氧基甲烷（DMM）是一项重要的转变。已使用密度泛函理论（DFT）计算对基于钴和钌的三膦催化剂进行了研究，以了解CO转化为DMM的反应机理途径以及基于贵金属/非贵金属的催化剂的作用。由于发现甲酸甲酯（MF）和甲氧基甲烷（MM）是重要中间体，因此已依次对该反应通过这些中间体进行了研究。对于CO和MF的氢化反应，已对诸如H和甲醇等氢源进行了研究。所有可能途径的计算反应自由能垒表明，两种氢源对钴-三膦催化剂都很重要。然而，在钌-三膦催化剂的情况下，计算得出分子H是唯一的氢源。还探索了各种酯化和缩醛化的可能性，以找到CO转化为DMM的最有利途径。我们发现氢化物向CO的转移是整个反应的速率决定步骤（RDS）。我们的机理研究表明，金属中心是催化的活性部分，而不是布朗斯特酸，氧化还原三膦配体通过推挽机制发挥重要作用。实施的微观动力学研究表明，该反应也非常依赖于气态反应物的浓度，并且在363 K以上速率常数呈指数增加。
