Spectroscopic studies of methanol decomposition on Pd[lcub]111[rcub]

The thermal decomposition of methanol on a clean Pd[lcub]111[rcub] surface has been investigated using X-ray photoelectron spectrometry (XPS), secondary ion mass spectrometry (SIMS) and thermal desorption spectrometry (TDS). In this work, we observe that the methanolic C-O bond activation on Pd[lcub]111[rcub] is a strongly coverage dependent process. At lower and higher coverages, XPS data suggest that CH₃O_ads is the principle product. At near monolayer coverage the methanolic C-O bond dissociates at 175 K to produce CH_3,ads, which is characterized by a C 1s binding energy of 283.8 eV, and is stable up to 400 K. A stepwise dehydrogenation of CH_3,ads to form CH_2,ads (methylene) and CH_ads (methylidyne) is observed above 400 K. Surface methyl and its dehydrogenated forms are characterized both by the chemical shift of the XPS C 1s peak from 283.8 to 284.8 eV and by positive ion SIMS peaks with m e = 15, 14 and 13. The gaseous products detected by TDS are methanol, CO, hydrogen, methane and water. This observation implies that the methanolic C-O bond cleavage is contingent upon a special molecular arrangement of precursors before reaction and that the CH_3,ads product is stabilized by ancillary reaction products, such as CO.