ADSORPTION AND DECOMPOSITION OF METHANOL ON TIO2, SRTIO3 AND SRO

The adsorptive and reactive behaviour of TiO2, SrTiO, 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 H-2 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 H-2 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.