Structural Properties of Gas-Phase Molybdenum Oxide Clusters [Mo{sub 4}O{sub 13}]{sup 2−}, [HMo{sub 4}O{sub 13}]{sup −}, and [CH{sub 3}Mo{sub 4}O{sub 13}]{sup −} Studied by Collision-Induced Dissociation

• Published in: Journal of the American Society for Mass Spectrometry 2019-10, Vol.30 (10)
• Main Authors: Plattner, Manuel, Baloglou, Aristeidis, Ončák, Milan, Linde, Christian van der, Beyer, Martin K.
• Format: Article
• Language: English
• Subjects: ATOMS; CARBON MONOXIDE; CATALYSIS; CATALYSTS; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; FORMALDEHYDE; HYDROGEN; MASS; MOLYBDENUM OXIDES; TOLUENE
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1007/s13361-019-02294-4

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 [Mo{sub 4}O{sub 13}]{sup 2−}, [HMo{sub 4}O{sub 13}]{sup −}, and [CH{sub 3}Mo{sub 4}O{sub 13}]{sup −} 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 MoO{sub 2} 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 [Mo{sub 4}O{sub 13}]{sup 2−} and [HMo{sub 4}O{sub 13}]{sup −}, dissociation requires opening or rearrangement of the ring structure, which is quite facile for the doubly charged [Mo{sub 4}O{sub 13}]{sup 2−}, but energetically more demanding for [HMo{sub 4}O{sub 13}]{sup −}. In the latter case, the hydrogen atom is found to stay preferentially with the negatively charged fragments [HMo{sub 2}O{sub 7}]{sup −} or [HMoO{sub 4}]{sup −}. The doubly charged species [Mo{sub 4}O{sub 13}]{sup 2−} loses one MoO{sub 3} unit at low energies while Coulomb explosion into the complementary fragments [Mo{sub 2}O{sub 6}]{sup −} and [Mo{sub 2}O{sub 7}]{sup −} dominates at elevated collision energies. [CH{sub 3}Mo{sub 4}O{sub 13}]{sup −} affords rearrangements of the methyl group with low barriers, preferentially eliminating formaldehyde, while the ring structure remains intact. [CH{sub 3}Mo{sub 4}O{sub 13}]{sup −} also reacts efficiently with water, leading to methanol or formaldehyde elimination. .