DECOMPOSITION OF GASEOUS ACETIC-ACID ON SNO2

Various methods have been used to study the reactions of acetic acid on SnO2 surfaces. A sensitive mass spectrometer was used in thermal desorption spectroscopy (TDS) and in reactive scattering experiments. The oxide surfaces were characterized by X-ray photoemission spectroscopy (XPS) and Auger electron spectroscopy (AES), and electrical conductance was used to monitor changes in the electron density caused by surface reactions. SnO2 catalysts were prepared as single crystals, sintered layers and thin films without any addition. Between room temperature and ca. 800 K reactions were observed in ultrahigh vacuum (UHV) and in air. A variety of desorbing molecules was found including acetic acid, ketene, methane, water, carbon monoxide and carbon dioxide. Carbon deposition was observed. In addition to the increase of conductance by exposure to acetic acid, a transient decrease was found within a limited temperature range. These results are interpreted by means of reaction models. For some oxidation processes oxygen atoms are extracted from the surface, generating oxygen vacancies which can be refilled. The possibility of a conductivity-based chemical sensor for gaseous acetic acid in air was demonstrated.