STRUCTURAL DEPENDENCE OF THE SELECTIVITY OF FORMIC-ACID DECOMPOSITION ON FACETED TIO2 (001) SURFACES Academic Article uri icon

abstract

  • The reactions of formic acid on Ti02 (001) single-crystal surfaces were examined by temperature-programmed desorption and X-ray photoelectron spectroscopy. The (Oil(-faceted and fll4)-faceted surfaces were chosen as model surfaces in order to investigate the effects of surface structure and composition upon reaction selectivity and to identify the active sites. Formic acid adsorbed dissociatively at 300 K to yield surface formate species. Approximately 15% of the adsorbed formates was removed from the surface as formic acid at 390 K via recombination with surface hydroxyls. The remaining formates decomposed above 550 K to CO, CO2, and formaldehyde, with selectivities toward these products dependent upon the surface structure and composition. On the (011)-faceted surface, which exposes fivefold oxygen-coordinated Ti4+ cations, adsorbed formates decomposed exclusively via unimolecular reactions to product CO and CO2. On the (1141-faceted surface, which exposes four-, five-, and sixfold coordinated cations, the reaction of adsorbed formates to produce formaldehyde was also observed. The net reduction of formic acid to formaldehyde on this surface was directly analogous to the bimolecular ketonization of higher carboxylates, which occurs exclusively on the (114}-faceted reconstruction of the (001) surface. Thus formaldehyde production from formic acid on this surface can be assigned to the disproportionation of two formates coordinated to a common Ti4+ cation of fourfold oxygen coordination. Unimolecular decomposition occurs for formates bound to fivefold coordinated cations, as it does for the higher carboxylates. 1990 American Chemical Society. all right reserved. 1990, American Chemical Society. All rights reserved.

published proceedings

  • LANGMUIR

author list (cited authors)

  • KIM, K. S., & BARTEAU, M. A.

citation count

  • 96

complete list of authors

  • KIM, KS||BARTEAU, MA

publication date

  • September 1990