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Methane activation by metals and semiconductors. Molecular orbital theory. Annual report, September 1987-August 1988

Technical Report ·
OSTI ID:6538431
An atom-superposition and electron delocalization molecular orbital study was made of CHn and CO reactions over coordinatively unsaturated Mo(IV) edge cations in MoS2. Coupling to C2H6 and C2H5(a) proceed with high barriers. CH2(a) coupling to strongly adsorbed ethylene proceeds with a lower barrier, and hydrogenation to ethane is possible. CO binds relatively weakly to 5-fold coordinated Mo and strongly to 4-fold coordinated sites. Over two such sites, CO easily tilts to a di-Sigma bridging orientation and dissociates with a low barrier. In the Fischer-Tropsch process hydrogenation to CH3(ads) and H2O(g) is expected. CO inserts into the Mo-CH3 bond with a low barrier, and subsequent hydrogenations to form C2H6+H2O or CH3CH2OH are favorable. It is proposed that the selectivity toward alcohol formation over alkali-doped MoS2 (the DOW process) may stem from the ability of the alkali cations to stabilize alkoxy intermediates. A second molecular orbital study shows AlN behaves similarly to MgO toward CH4. Stoichiometric AlN is inactive. CH4 is activated by surface N(2-) hole sites, forming surface HN(2-) and methyl radicals.
Research Organization:
Case Western Reserve Univ., Cleveland, OH (USA). Dept. of Chemistry
OSTI ID:
6538431
Report Number(s):
PB-89-131163/XAB
Country of Publication:
United States
Language:
English