Oxygen-Isotope Exchange between CO2 and Solid Ti18O2

The light-induced oxygen-isotope exchange between gaseous CO2 and solid (TiO2)-O-18 (anatase) and the spontaneous thermal isotope exchange that takes place between the vacuum-calcined solid (TiO2)-O-18 and CO2 were studied by gas-phase high-resolution Fourier transform infrared absorption spectroscopy over a period of several days. The absorption rovibrational spectra of all the measured carbon dioxide isotopologues were assigned and served as the quantification of the time-dependent isotope exchange between the oxygen atoms from the (TiO2)-O-18 solid and the oxygen related to the gaseous CO2. The (CO2)-O-18 was formed as the dominating final product with a minor content of (COO)-O-16-O-18. The rate of oxygen-isotope exchange is highly sensitive to the conditions of the titania pretreatment; vacuum-annealed (TiO2)-O-18 at 450 degrees C exhibited a very high spontaneous oxygen exchange activity with gaseous (CO2)-O-16. A mechanism for the O-18/O-16 exchange process is discussed at the molecular level. The photo catalytic formation of methane, acetylene, and (CO)-O-16 released from the (TiO2)-O-18 surface was observed after irradiation by an excimer laser.