Role of O/sup -/ surface radicals for methane CH bond activation and subsequent reactions on MoO/sub 3/: molecular orbital theory

Journal Article · Thu May 21 04:00:00 EDT 1987 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100295a056· OSTI ID:6367930

Mehandru, S P; Anderson, A B; Brazdil, J F; Grasselli, R K

A molecular orbital study is made of the reaction of methane with O/sup -/ hole centers on the surface of MoO/sub 3/. The following predictions are made. When the O/sup -/ is created by a UV O 2p ..cap alpha.. Mo 4d charge-transfer excitation, heterolytic products, OH/sup -/ and Mo/sub V/ x CH/sub 3/, form readily at the edges of the crystals where unsaturated molybdenum sites are present. Deexcitation to OH/sup -/ and Mo/sup VI/:CH/sub 3//sup -/ is expected to proceed rapidly and a side reaction to slightly less stale homolytic products, OH/sup -/, 2Mo/sup V/, and OCH/sub 3//sup -/, may also take place, preventing deexcitation so that Mo/sup V/ is not oxidized to Mo/sup VI/, so that the excitation energy may be said to be chemically stored. The CH bond activation barrier is calculated to be 0.7 eV. Activation is a consequence of a stabilizing 3-centered CH-O/sup -/ sigma-donation interaction, the antibonding counterpart of which takes the hole and is occupied by only one electron in the transition state. If a second electron-hole pair is formed, the methyl radical can shift to the O/sup -/ center with a slight loss in stability, and the surface is reduced by two electrons. The methyl cation which is formed can be viewed as a methyl radical which has promoted an electron to a nearby Mo/sup VI/. Once the methyl radical moves to a basal plane of the crystal, which is covered entirely by oxygen anions, it diffuses with a low approx.0.4-eV barrier.

• Research Organization: Case Western Reserve Univ., Cleveland, OH
• OSTI ID: 6367930
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 91:11; ISSN JPCHA
• Country of Publication: United States
• Language: English

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ALCOHOLS
ALDEHYDES
ALKANES
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTIONS
DATA
ELECTRONIC STRUCTURE
FORMALDEHYDE
HYDROCARBONS
HYDROXY COMPOUNDS
INFORMATION
MATHEMATICAL MODELS
METHANE
METHANOL
MOLECULAR MODELS
MOLECULAR ORBITAL METHOD
MOLECULAR STRUCTURE
MOLYBDENUM COMPOUNDS
MOLYBDENUM OXIDES
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
REFRACTORY METAL COMPOUNDS
THEORETICAL DATA
TRANSITION ELEMENT COMPOUNDS