Interaction of HCOOH with stoichiometric and reduced SrTiO3(100) surfaces

Abstract

Interaction of formic acid with stoichiometric (TiO2-terminated) and reduced SrTiO3(100) surfaces has been investigated using temperature programmed desorption (TPD), and x-ray photoelectron spectroscopy (XPS). Formic acid was dissociated to form formate and a surface proton below 250 K on both stoichiometric and reduced SrTiO3(100) surfaces. Formate was decomposed primarily through dehydration to produce CO and H2O, instead of through dehydrogenation to produce CO2 and H2, on both surfaces. Formaldehyde produced from decomposition of formate was also observed on both surfaces. On stoichiometric surfaces, formaldehyde was produced through bimolecular coupling of two formates on low-coordination Ti cation sites. However, on the reduced surface, formaldehyde formation involves the reduction of surface formates through the oxidation of reduced Ti cations. XPS results show that surface defects on reduced SrTiO3(100) surfaces were reoxidized significantly upon exposure to 30 L HCOOH at 300 K, in contrast to defects on reduced TiO2(110) surfaces where no reduction in defect intensity was observed under identical conditions. The TPD peak of formaldehyde on a reduced SrTiO3(100) surface is shifted to lower temperature and is significantly broader (down to below 300 K) compared to on the stoichiometric surface. The adsorption and decomposition of HCOOH on SrTiO3(100) surfaces are compared with those on TiO2 surfaces.