This study investigated the photocatalytic reduction of CO2 in a self-designed closed circulated batch reactor system and a bench-scale batch photocatalytic reactor. The photocatalysts tested included titanium dioxide (TiO2, Degussa P-25) and zirconium oxide (ZrO2). The reductants investigated included hydrogen (H2), water vapor (H2O), and hydrogen plus water vapor (H2+H2O). The wavelengths of incident near ultra-violet (UV) and UV lights for the photocatalysis of TiO2 and ZrO2 were 365 nm and 254 nm, respectively. The initial concentrations of CO2 ranged from 0.2-5.0% and the reaction temperature ranged from 35-95 ¡³C. The incident near-UV (or UV) light with wavelength of 365 nm (or 254 nm) was irradiated by a 15-watt low-pressure mercury lamp. The photocatalytic reaction was conducted continuously for approximately two hours. Reactants and products were analyzed by a gas chromatography with a flame ionization detector followed by a methanizer (GC/FID-methanizer). Experimental results indicated that glass pellets coated with TiO2 had better photoreduction efficiency than ZrO2. The highest yield rates of the photoreduction of CO2 were obtained using TiO2 with H2+H2O and ZrO2 with H2. Photoreduction of CO2 over TiO2 with H2+H2O formed CH4, C2H6, and CO in the yield of 32.95~94.60, 0.80~18.55, 1.12~21.78 £gmol/g, respectively, while the photoreduction of CO2 over ZrO2 with H2 formed CO in the yield of 0.34~4.99 £gmol/g. Results obtained from the operating parameter tests showed that the photoreduction rate increased with the initial concentration of carbon dioxide and resulted in more product accumulation. The photoreduction rate of carbon dioxide increased with reaction temperature, which promoted the formation of products. Concurred with previous researches, the reaction rate of major products over TiO2 and ZrO2 were higher than previous investigations of CO2 photoreduction. Furthermore, the spectra of FTIR showed that formic acid (HCOOHads), methanol (CH3OHads), carbonate (CO32−ads), bicarbonate (HCO32−ads), formate (HCOO−ads), formic acid (HCOOH ads), formaldehyde (HCOHads) and methyl formate (HCOOCH3 ads) formed on the surface of TiO2 and ZrO2 photocatalysts. The detected reaction products supported the proposal of two reaction pathways for the photoreduction of CO2 over TiO2 and ZrO2 with H2 and H2O, respectively. A modified bimolecular Langmuir-Hinshelwood kinetic model was developed to simulate the reaction temperature, CO2 initial concentration and relative humidity promotion and inhibition of the photoreduction of CO2. Additionally, the modified L-H kinetic model was successfully applied to simulate the photoreduction rate of CO2. The result showed that CO2 could be reduced by used solar light over TiO2 and ZrO2 photocatalysts. The reaction products of CO2 photoreduction over TiO2 were CH4, C2H6, and CO in the yield of 2.16~2.995, 0.057~0.128, 0.078~0.134 £gmol/g, respectively, while the photoreduction of CO2 over ZrO2 formed only CO in the yield of 0.023~0.051 £gmol/g. Furthermore, experimental results indicated that TiO2 gave the highest average photo energy efficiency (AEf) of ~4.13%, and apparent quantum efficiency (£pA) of ~1.05%. However, the ZrO2 gave the highest average photo energy efficiency (AEf) of 5.07¡Ñ10-3%, and apparent quantum efficiency (£pA) of ~1.54¡Ñ10-2%.

This study combined photocatalytic technology with activated carbon cellulose-paper filter (ACCF) adsorption to decompose gaseous pollutants. Gaseous pollutants were initially adsorbed by activated carbon and could be further decomposed by photocatalytic technology. This study selected acetone (CH3COCH3) as gaseous pollutants. Two market available photocatalysts (photocatalysts¢¹and¢º) were coated on ACCF by impregnation to decompose acetone in a batch photocatlytic reactor. Operating parameters investigated in this study included initial acetone concentration (4.1~10.2 £gM), reaction temperature (40~70¢J), and water vapor (0~20 %). The incident UV light of 365 nm was irradiated by a 20-watt low-pressure mercury lamp placing above the batch photocatalytic reactor. The ACCF coated with TiO2 was placed at the center of the photocatalytic reactor. Acetone was injected into the reactor by a gasket syringe to conduct the photocatalytic tests. Reactants and products were analyzed quantitatively by a gas chromatography with an electron capture detector (GC/DCD) and a flame ionization detector followed by a methaneizer (GC/FID-Methaneizer). Finally, a Langmiur-Hinshewood (L-H) kinetic model was proposed to describe the rate of photocatalytic reaction. Results obtained from the photocatalytic tests indicated that photocatalyst¢º was better than photocatalyst¢¹ for the decomposition of acetone. Experimental results indicated that the size range of self-produced TiO2 photocatalyst by sol-gel was 20~70 nm. The end products were mainly CO and CO2, which resulted in the mineralization ratio up to 98%. Results obtained from the operating parameter tests revealed that the increase of initial acetone concentration enhanced the amount of acetone adsorbed on ACCF, which however did not increase the reaction rate of acetone. Although the increase of reaction temperature could reduce the amount of acetone adsorbed on ACCF, the decomposition rate of acetone could be promoted, so as the yield rate and mineralization ratio of products (CO and CO2). The increase of water vapor could slightly decrease the amount of acetone adsorbed on ACCF. The competitive adsorption phenomenon between acetone and water molecules on active sites could decelerate the decomposion of acetone. Moreover, the ACCF would not be saturated since the adsorbed acetone could be further decomposed quickly by the photocatalysts, which made the TiO2/ACCF more effective on removing acetone and lasted longer than the conventional ACCF. Finally, a modified bimolecular Langmuir-Hinshelwood kinetic model was developed to investigate the influences of initial acetone concentration reaction, temperature, and relative humidity on the promotion and inhibition for the photocatalytic oxidation of acetone. The modified L-H kinetic model could successfully simulate the photocatalytic reaction rate of acetone. Thus, the reaction rate of acetone over TiO2/ACCF could be described by the modified L-H kinetic model.