Photooxidation of CH3C1on TiO2(110) Single Crystal and Powdered TiO2 Surfaces

摘要

The photooxidation of CH3C1 on TiO2 has been investigated using two approaches.In the first, TiO2(110) (rutile) containing oxygen anion vacancy defect sites has been studied using temperature-programmed desorption to follow the production of photooxidation products. In the second approach, powdered TiO2 (mainly anatase) has been studied using transmission infrared spectroscopy. On TiO2(110) the observed producers are H2CO, CO, H2O, and HC1. On powdered TiO2, the products are CO, CO2, H2O (as surface OH groups), HC1, and CH2Cl2. The dissimilarities are postulated to be due to two factors: (1) different surface site distributions for the two types of TiO2 surface; (2) higher pressure of reactants in the powdered TiO2 investigation. Both sets of experiments were done in the absence of water and demonstrate that water is unnecessary for the photooxidation reaction. However, O2 is crucial for the photooxidation of CH3C1. The formation of CH2C12 as one of the photooxidation products over powdered TiO2 suggests that a free-radical-mediated mechanism exists in this case. jg.