Takashi Kawabe

Chemisorbed Oxygen Species over the (110) Face of SnO2

The electronic states of chemisorbed oxygen species on the (110) face of SnO2 and their variations caused by heat treatments and/or O2 exposure have been investigated. The reactivities of the chemisorbed oxygen species for methane oxidations were also examined.Four different chemisorbed oxygen species (O22-, O2-, O-, Ob) were observed, in addition to the lattice oxygen (O2-), on the surface of the stabilized (110) surface of SnO2 after O2 exposure. The Ob species was assumed to be the bridging oxygen at the topmost layer of the SnO2 (110) surface having no neighboring oxygen vacancies. The electronic state of Ob was converted to O- upon CH4 exposure at 473 K by coupling with newly produced vacancies at the bridging site of the SnO2 (110) surface.

Morphological effects of SnO2 thin film on the selective oxidation of methane

The morphological effects of SnO 2 thin film on catalytic activities and selectivities for the selective oxidation of CH 4 were investigated with X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). Dense texture type and a columnar texture type SnO 2 thin films were prepared by the sputtering method. The measured proportion of adsorbed oxygen species (O 2- , O 2 2- , O 2 - and O b ) on these two types of samples with XPS were different from each other, and the proportion of a highly reactive oxygen species O - was larger on the dense sample. The TDS data of the products (HCHO, CH 3 OH, CO, CO 2 and H 2 O) were obtained on the two different structured film samples after CH 4 exposure at room temperature. The obtained TPD data were explained appropriately by considering several reaction pathways. The dense texture type SnO 2 film showed a higher reactivity for the oxidation of CH 4 than that of the columnar texture type one. The selective formation of HCHO was especially observed for the dense texture film. The oxidation of CH 4 was therefore strongly affected by the surface morphology of SnO 2 film.

Methanol adsorption on an oxidized and a reduced SnO2 thin film

Abstract The effects of surface structures of SnO 2 thin films on the selective dissociation of methanol have been investigated with X-ray photoelectron spectroscopy. A pre-oxidized surface of SnO 2 was in favor of the abstraction of hydrogen from methanol while a highly defective surface of SnO 2 prepared by Ar-ion etching favored the dissociation of the CO bond in methanol. The surface, therefore, of pre-oxidized SnO 2 reacted as Bronstead base sites but the surface of highly defective SnO 2 reacted as Bronstead acid sites. These results clearly show the importance of surface structures in the selection of the acid/base interaction of methanol on the SnO 2 surface.