Activation of Methane by Tungsten Carbide and Nitride Cluster Cations

Gas-phase reactions of tungsten carbide and nitride cluster cations, WC⁺ (n = 1-5, m ≤ 5) and WN⁺ (n = 1-6, m ≤ 2), with methane are investigated at near thermal energies. Most of the clusters react readily with CH₄ to form WCH₂⁺ or WNCH₂⁺ under single collision conditions, in contrast to the almost no reactivity of pure tungsten clusters. This result indicates that the introduction of carbon or nitrogen atoms can enhance the reactivity of tungsten clusters toward the CH₄ dehydrogenation. In addition, the formation and the release of an ethylene molecule are strongly suggested in the reaction of WC⁺ with CH₄ as a minor reaction channel. Nearly all the nitride cluster cations, WN⁺ (n ≥ 2), exhibit higher reactivity than their corresponding carbides, WC⁺, whereas WN⁺ is less reactive than WC⁺. Furthermore, the multiple collision reactions of the highly reactive tungsten nitride species such as WN⁺ and W₄N⁺ lead to the formation of WNCH₂⁺ (x = 2, 3), which shows that the dehydrogenation of more than one CH₄ molecule occurs.