| Summary: | 碩士 === 國立中興大學 === 環境工程學系 === 89 === Abstract
This investigation used a tube reactor deposited TiO2 thin film inside by chemical vapor deposition (CVD) method and installed a UV lamp with 365 nm wavelength to study the heterogeneous photocatalytic reaction of gasous toluene. SEM and XRD were used to analyse the size and crystal structure of catalyst under different reactive temperature and annealing temperature. The influence of the parameters controlled in the photocatalytic reaction including concentration of reactant, flowrate, humidity, oxygen contain and light intensity was investigated in this research. The intermediates of reacton in gas phase and on the surface of catalyst were monitored by FTIR in order to propose the possible reaction mechanisms and pathways.
The X-ray analyses revealed that TiO2 film was amorphous when deposited at 200oC and had anatase polycrystalline structures when deposited at higher temperatures. We only found the rutile structure when the annealing temperature at 850oC. The best effect of conversion with toluene was reactive temperature at 350oC and annealing temperature at 550oC.
Catalyst deactivation was observed when air containing toluene and water was irradiated by UV lamp for 8 minutes. After irradiating without feeding mixture gas for 30 minutes, the catalyst was regenerated. According to the experimental results, the reaction rate decreased with increasing flowrate. The reaction rate decreased with increasing humidity, indicating moisture inhibited the decomposition of toluene. The reaction rate increased with the increasing oxygen contain. However, when the oxygen contain was higher than 20%(v/v), the reaction was not affected. The reaction rate increased with increasing concentration of toluene due to the increasing concentration gradient between bulk phase and TiO2 surface, but when it was more than 4.7μm, the reaction rate decreased, indicating that the result of catalyst deactivation. Increasing of the light intensity increased the number of photon and reaction rate.
Using FTIR to analyze the gas phase, the CO2 and H2O molecules increased as time went by, and observed the peaks which proposed to be benzaldehyde, benzene and phenol. The molecules of toluene was adsorbed on TiO2 surface with the weak physical bond and could be desorbed by outgassing at —756 torr. After illuminating with UV lamp, we found amount of —COOH groups, indicating the accumulation of benzoic acid which had relationship with the catalyst deactivation. When illumination at —756 torr was remained, the spaces of accumulation on the surface of TiO2 film didn’t change anymore within one minute. We observed that —OH group and —COOH group decreased and the —C6H5 group and the CO2 increased, indicating that benzoic acid was photocatalyzed to become C6H6 and CO2.
|
|---|
