Adsorption and decomposition of methanol on TiO2, SrTiO3 and SrO

Abstract

The adsorptive and reactive behaviour of TiO₂, SrTiO₃ and SrO towards methanol have been investigated using temperature-programmed desorption and XPS. TiO₂ was found to be reduced during the adsorption/desorption process and showed predominantly CH₄ formation at low coverages. At higher coverages, alternative paths led also to the desorption of CH₃OH and HCHO though CH₄ was the main product desorbed at ca. 500 K. The product pattern indicates that a methoxy is the major surface intermediate. CO and H₂ were evolved at ca. 600 K, possibly from the decomposition of a formate species, while H₂O was desorbed between 300 and 700 K. On SrO the coincident evolution of CO and H₂ at 580 K, with H₂O and CO₂ being minor products, indicated a formate intermediate as the dominant one on this surface. The product pattern on SrTiO₃ resembled that on TiO₂, although the main product in this case was CH₃OH, with CH₄ being produced in much smaller quantities and only at much higher temperature than on TiO₂(620 K). The source of these differences is discussed in terms of the defect chemistry of the surfaces involved.