Reactions of methyl groups on a non-reducible metal oxide: The reaction of iodomethane on stoichiometric α-Cr2O3(0001)

• Published in: Surface science 2015-11, Vol.641, p.148-153
• Main Authors: Dong, Yujung, Brooks, John D., Chen, Tsung-Liang, Mullins, David R., Cox, David F.
• Format: Article
• Language: English
• Subjects: Cr2O3; Dehydrogenation; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Methyl iodide; TPD; XPS
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2015.06.003

The reaction of iodomethane on the nearly stoichiometric α-Cr2O3(0001) surface produces gas phase ethylene, methane, and surface iodine adatoms. The reaction is initiated by the dissociation of iodomethane into surface methyl fragments, −CH3, and iodine adatoms. Methyl fragments bound at surface Cr cation sites undergo a rate-limiting dehydrogenation reaction to methylene, =CH2. The methylene intermediates formed from methyl dehydrogenation can undergo coupling reactions to produce ethylene via two principle reaction pathways: (1) direct coupling of methylene and (2) methylene insertion into the methyl surface bond to form surface ethyl groups which undergo β-H elimination to produce ethylene. The liberated hydrogen also combines with methyl groups to form methane. Iodine adatoms from the dissociation of iodomethane deactivate the surface by simple site blocking of the surface Cr3+ cations. [Display omitted] •Methyl iodide dissociates to surface methyl, −CH3, and I adatoms on α-Cr2O3(0001).•The primary reaction of methyl is rate-limiting dehydrogenation to methylene, followed by methylene coupling to ethylene, CH2=CH2, or methyl hydrogenation to methane.•XPS and DFT indicate that methyl species bind at both surface cation and anion sites.