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.

SUBMITTER: Plattner M 

PROVIDER: S-EPMC6805806 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature