Photoreduction of Carbon Dioxide in a Batch Reactor Using Nanosized Titanium Dioxide Photocatalysts Prepared by a Sol-gel Method
The increase of carbon dioxide (CO2) concentration in the atmosphere has become a severe environmental problem, since it could cause global warming due to greenhouse effects. Thus, the reduction of CO2 emission to tackle the greenhouse effect has become one of the most important tasks for sustainable development. The outcomes of this study would be valuable to evaluate the feasibility of applying photocatalytic reduction process to remove CO2 from the atmosphere as well as the flue gas.
This study investigated the photocatalytic reduction of CO2 in a self-designed batch UV/TiO2 photocatalytic reactor. The photocatalysts tested included commercial TiO2 (Degussa P-25) and synthesized TiO2 via modified sol-gel process (i.e. NO3-/TiO2 and SO42-/TiO2). Stainless steel supports coated with TiO2 were packed in the batch reactor. The initial concentrations of CO2 ranged from 0.5% to 7.5%. The reductants investigated included hydrogen (H2), water vapor (H2O), and hydrogen with water vapor (H2+H2O). The incident UV light with wavelength of 365 nm was irradiated by a 15-watt low-pressure mercury lamp. The photocatalytic reaction was conducted continuously for approximately 48 hours. Reactants and products were analyzed quantitatively by a gas chromatography with a flame ionization detector followed by a methaneizer (GC/FID-Methaneizer).
Experimental results indicated that stainless steel coated with TiO2 had better photoreduction efficiency than that of quartz glass. The optimal operating conditions of CO2 photoreduction were observed by using H2 over SO42-/TiO2, which could produce major products of CO and CH4 and minor products of C2H4 and C2H6. Sulfuric acid used as a stabilizer in the sol-gel process could produce TiO2 of high specific surface area. 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. Higher photoreduction efficiency of carbon dioxide was observed by using the hydrogen (H2) than water vapor (H2O). The photoreduction rate of carbon dioxide increased with reaction temperature, which promoted the formation of products. In addition, proper water vapor (ie. relative humidity of water vapor =25%~75%) could increase the photoreduction efficiency. However, the photoreduction efficiency decreased white it was close to (ie. relative humidity of water vapor =75%~100%).
Concurred with previous researches, the reaction rate of major products over SO42-/TiO2 were higher than previous investigations of CO2 photoreduction. This study proposed the reaction pathway using hydrogen and/or water vapor as the reductants. Moreover, a one-site Langmiur-Hinshewood kinetic model (L-H model) was successfully applied to simulate the reaction rate of CO2 during the photoreduction reaction process.
Advisor:jjliang; Chung-Shin Yuan; Ming-Shean Chou; Hung, C.-H.
School:National Sun Yat-Sen University
School Location:China - Taiwan
Source Type:Master's Thesis
Keywords:product analysis model development reaction pathway operating parameters photocatalysts sol gel process photoreduction carbon dioxide
Date of Publication:08/20/2004