Kinetic studies of the decomposition of CH3COOH and CH3COOD on SnO2 single crystals

Abstract The decomposition of CH 3 COOH, CH 3 COOD, and CH 4 on as grown SnO 2 (101) faces, cleaned in UHV, was investigated by reactive scattering, thermal desorption spectroscopy (TDS), and four-probe surface conductivity measurements. After exposure to methane and acetic acid in TDS CO and CO 2 appear in a similar way. The spectra are different from the ones after exposures to CO. These findings are conceivable assuming a formate intermediate in equilibrium with CO and CO 2 . This mechanism is known from the water gas shift reaction on ZnO. It implies a reaction of the methyl group of the acetic acid with lattice oxygen delivering surface hydrogen. On exposure to CH 3 COOD also desorption of CH 3 COOH, CH 4 and H 2 O is observed. This exchange of H/D can only be caused by a decomposition of the methyl group. A complete reaction scheme is proposed explaining also a reversible and an irreversible increase of surface conductivity by hydrogen donors and oxygen vacancy donors, respectively.