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首页> 外文期刊>Chemistry: A European journal >Methane Activation by Diatomic Molybdenum Carbide Cations
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Methane Activation by Diatomic Molybdenum Carbide Cations

机译：双原子碳化钼阳离子对甲烷的活化

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摘要

Metal carbide species have been proposed as a new type of chemical entity to activate methane in both gas-phase and condensed-phase studies. Herein, methane activation by the diatomic cation MoC~+ is presented. MoC~+ ions have been prepared and mass-selected by a quadrupole mass filter and then allowed to interact with methane in a hexapole reaction cell. The reactant and product ions have been detected by a reflectron time-of-flight mass spectrometer. Bare metal Mo~+ and MoC_2H_2~+ ions have been observed as products, suggesting the occurrence of ethylene elimination and dehydrogenation reactions. The branching ratio of the C_2H4 elimination channel is much larger than that of the dehydrogenation channel. Density functional theory calculations have been performed to explore in detail the mechanism of the reaction of MoC~+ with CH4. The computed results indicate that the ethylene elimination process involves the occurrence of spin conversions in the C-C coupling (doublet!quartet) and hydrogen atom transfer (quartet! sextet) steps. The carbon atom in MoC~+ plays a key role in methane activation because it becomes sp~3 hybridized in the initial stages of the ethylene elimination reaction, which leads to much lower energy barriers and more stable intermediates. This study provides insights into the C-H bond activation and C-C coupling involved in methane transformation over molybdenum carbide-based catalysts.
机译：在气相和冷凝相研究中，已经提出金属碳化物作为一种新型的化学实体来活化甲烷。在此，提出了由双原子阳离子MoC〜+活化的甲烷。已经制备了MoC +离子，并通过四极质量过滤器对其进行了质量选择，然后使其在六极反应池中与甲烷相互作用。反应物和产物离子已通过反射式飞行时间质谱仪检测到。观察到裸金属Mo〜+和MoC_2H_2〜+离子为产物，表明发生了乙烯消除和脱氢反应。 C_2H4消除通道的支化比远大于脱氢通道的支化比。进行了密度泛函理论计算，以详细探讨MoC〜+与CH4反应的机理。计算结果表明，乙烯消除过程涉及在C-C偶联（二重四联体）和氢原子转移（四重六联体）步骤中发生自旋转化。 MoC〜+中的碳原子在甲烷活化中起关键作用，因为它在乙烯消除反应的初始阶段与sp〜3杂化，从而导致更低的能垒和更稳定的中间体。这项研究提供了对基于碳化钼的催化剂进行甲烷转化所涉及的C-H键活化和C-C偶联的见解。

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