X-ray photoelectron spectroscopy study of the interaction of methanol with polycrystalline copper oxide surface
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X-ray photoelectron spectroscopy study of the interaction of methanol with polycrystalline copper oxide surface S. Badrinarayanan,a) A. B. Mandale, and S. R. Sainkar Special Instruments Division, National Chemical Laboratory, Pune 411008, India (Received 4 January 1995; accepted 4 March 1996)
Methanol decomposition on a clean polycrystalline copper oxide surface was studied by x-ray photoelectron spectroscopy (XPS). Methanol was adsorbed at 133 K and desorbed over a broad temperature range. When CuO was exposed to a very low dose of methanol vapor, dissociative adsorption takes place, leading to the formation of CH3 O and H2 O. This is attributed to the presence of preadsorbed oxygen on the CuO surface.
Many XPS studies of methanol decomposition on metal and oxide surfaces1–10 have been reported in the literature. Only a few attempts have been made to study the adsorption of methanol on polycrystalline oxides.6 In most of these studies, methanol was adsorbed at a very low temperature (100–150 K) and the substrate was heated to various temperatures. This communication describes the results of our XPS investigation on the adsorption of methanol on polycrystalline copper oxide (CuO) powder. The relevant experimental details for XPS measurements and the analysis of the results are given in our earlier study.11 The experiments were carried out under two different experimental conditions. (i) Methanol (, 5 L, 1 L 1026 Torrys) was adsorbed at 113 K, and the photoelectron spectra (PES) were recorded at various temperatures. (ii) Several monolayers of methanol were condensed on the copper oxide surface, and the desorption was carried out at various temperatures. The sequence of treatments is given in Table I. Using the BE values, the intensity ratio OyCu (calculated using the peak area and the photoelectron cross section values), the ratio of the intensity of the satellite structure to Cu2p 3/2 level, and the kinetic energy of the Cu(LVV) Auger peak [Fig. 1(b), Table II], it is concluded that the fresh CuO surface is predominately Cu(OH)2 .12 After the treatment II it is completely converted to Cu2 O13,14 [Fig. 1(a)]. Subsequent heating in high purity oxygen completely converted this Cu2 O to CuO.12 The O1s peak became very broad after the treatment III, and this peak was resolved into two Gaussian components with BE values of 530.1 and 531.6 eV. The low BE peak is due to bulk oxide, and the 531.6 eV O1s peak is due to adsorbed oxygen species or defect region of the CuO surface rather than to OH. This reasoning is based on the fact that the CuO sample was not exposed to atmosphere before the completion a)
Address all correspondence to this author. J. Mater. Res., Vol. 11, No. 7, Jul 1996
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TABLE I. Details of treatments. Treatment I: High purity CuO. Treatment II: CuO heated in vacuum (673 K, 4 h). Treatment III: After treatment II, heated in oxygen (673 K, 760 Torr, 4 h) to get CuO. Treatment IV: Methanol was absorbed o
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