Structural Properties of Gas-Phase Molybdenum Oxide Clusters [Mo₄O₁₃]²⁻, [HMo₄O₁₃]⁻, and [CH₃Mo₄O₁₃]⁻ Studied by Collision-Induced Dissociation

Abstract

Molybdenum oxide-based catalysts are widely used for the ammoxidation of toluene, methanation of CO, or hydrodeoxygenation. As a first step towards a gas-phase model system, we investigate here structural properties of mass-selected [Mo4O13]2−, [HMo4O13]−, and [CH3Mo4O13]− by a combination of collision-induced dissociation (CID) experiments and quantum chemical calculations. According to calculations, the common structural motif is an eight-membered ring composed of four MoO2 units and four O atoms. The 13th O atom is located above the center of the ring and connects two to four Mo centers. For [Mo4O13]2− and [HMo4O13]−, dissociation requires opening or rearrangement of the ring structure, which is quite facile for the doubly charged [Mo4O13]2−, but energetically more demanding for [HMo4O13]−. In the latter case, the hydrogen atom is found to stay preferentially with the negatively charged fragments [HMo2O7]− or [HMoO4]−. The doubly charged species [Mo4O13]2− loses one MoO3 unit at low energies while Coulomb explosion into the complementary fragments [Mo2O6]− and [Mo2O7]− dominates at elevated collision energies. [CH3Mo4O13]− affords rearrangements of the methyl group with low barriers, preferentially eliminating formaldehyde, while the ring structure remains intact. [CH3Mo4O13]− also reacts efficiently with water, leading to methanol or formaldehyde elimination. Electronic supplementary materialThe online version of this article (10.1007/s13361-019-02294-4) contains supplementary material, which is available to authorized users.

Rearrangement and decomposition pathways of bare and hydrogenated molybdenum oxysulfides in the gas phase

“…38 The fragmentation pathways of molybdenum oxide clusters in the gas phase provide important additional information. 39 To obtain insight into catalytic properties of molybdenum oxysulfides, we investigate here their structure, flexibility and chemical reactivity as well as hydrogen adsorption/desorption through collision-induced dissociation of [Mo 2 O 2 S 6 ] 2− , [HMo 2 O 2 S 6 ] − and their fragments, as well as quantum chemical calculations. The results suggest that these species represent potential reactive intermediates in HER catalysis.…”

Decomposition of Halogenated Molybdenum Sulfide Dianions [Mo3S7X6]2–(X = Cl, Br, I)

“…Protonation in the gas phase followed by Coulomb explosion was probed in the reactions of [Mo 2 O 2 S 6 ] 2– and [Mo 2 O 2 S 5 ] 2– with organic acids . Further insight was gained by the comparison with the fragmentation pathways of molybdenum oxide and oxysulfide clusters.…”