Methane Activation by Diatomic Molybdenum Carbide Cations

Abstract

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 MoC2H2(+) ions have been observed as products, suggesting the occurrence of ethylene elimination and dehydrogenation reactions. The branching ratio of the C2H4 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.

Thermal Methane Conversion to Formaldehyde Promoted by Single Platinum Atoms in PtAl2O4− Cluster Anions

“…Only a few oxide species such as FeO + , [6,15] CoO + , [16] and NiO + [17] can react with methane to produce stable C 1 oxygenates methanol and formaldehyde. [2,3] It is noteworthy that in addition to oxides, oxygen-free species including atomic transition metal ions, [18] Au 2 + , [19] MoC + , [20] and so on [3,21] can also react with methane to generate stable molecules such as C 2 H 4 and H 2 .…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…1532, 1533) were observed by solid-state NMR after treatment of silica-bound carbyne complexes 1530, 1531 with trimethylphosphine [1316]. A computational study of molybdenum carbide catalyzed conversion of methane to ethylene or acetylene evoked several C-H activation of alkyl and hydride migration steps [1317]. As previously noted in the discussion of Group 6 metal carbene complexes, carbyne complex intermediates are involved in the transformation of silylene complexes to cyclic carbene complexes using episulfides [920].…”

Reactions of metal cluster anions with inorganic and organic molecules in the gas phase

“…15) has a large SD value of 1.59μ B , which corresponds to a significant overall activation barrier (0.10 eV). This study revealed that to cleave the C-H bonds through the OA mechanism, the unreactive ETM centers can be properly engineered to be reactive through carburization, 233,236 which explains the importance of the related metal carbides in heterogeneous catalysis. The dissociative-adsorption of CO onto Mo 2 C 2 − thus correctly manipulates the SD distribution on the metal centers and promotes the activation and transformation of methane.…”