Methanol decomposition on Ni(111): Investigation of the C-O bond scission mechanism

• Published in: Surface science 1987-05, Vol.183 (3), p.316-330
• Main Authors: Russell, J.N., Chorkendorff, I., Yates, J.T.
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Solid-gas interface; Surface physical chemistry
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/S0039-6028(87)80213-3

The possibility of a C-O bond scission mechanism in the decomposition of CH 3OH on Ni was examined by mole fraction analysis of the desorbing CO isotopes produced by the decomposition of an adsorbed mixture of 13CH 3 16OH and 12CH 3 18OH on a Ni(111) surface. No isotopic scrambling was observed on the clean, H-precovered, or sputter roughened Ni(111) surfaces. However, isotopic scrambling could be induced in the desorbing CO by Ar + sputtering the adsorbed mixture of methanol isotopes. Whether the C-O bond scission mechanism could be methanol-flux dependent was also explored. Carbon deposition at trace levels, a proposed consequence of C-O bond scission, was observed for high methanol fluxes ( F>1×10 16 cm −2 s −1). However, the small amount of carbon deposited was exposure rather than flux dependent and was due to low impurity levels in the methanol. We conclude that C-O bond scission for methanol on Ni(111) is not a viable elementary process under any of the methanol flux conditions explored, and that its maximum efficiency at 180 K is -2×10 13 cm −2 s −1), two H 2 desorption features are observed. The low temperature feature (370 K) results from desorptionlimited H 2 desorption and corresponds to the β 2-H 2 desorption feature from H/Ni. The high temperature feature (430 K) can be explained by accelerated methanol surface reactivity during exposure to methanol after blocked surface sites open by thermal desorption of CO. This differs from the proposed CH x (a) decomposition proposed by others as an explanation.