| Summary: | 碩士 === 國立臺灣大學 === 環境工程學研究所 === 94 === This study investigated the application of the ultra violet (UV) with reduction photocatalyst to convert the green-house air pollutants to the useful chemicals. The method is denoted as UV/photocatalyst process. Carbon dioxide, which has a highest concentration among green-house air pollutants was taken as a model compound. The emission of CO2 to the atmosphere was substantially found in the industrial waste gaseous streams. The operation parameters and influential factors such as the type, amount, and coating of photocatalysts, treatment temperature, initial concentration of CO2, intensity and wave length of UV radiation, type of solutions, and hydrogen sources, etc. were examined in order to find the proper conditions for the effective reduction of CO2 to useful chemicals. The photocatalyts used in this study were Ag/TiO2 and Cu/TiO2 made by the impregnation method. The wavelength of UV irradiation was 254 nm. The photocatalytic reductions of CO2 were performed via three different methods. In method 1, only gases CO2 was presented in the reactor to process the phtocatalytic reaction with catalyst on glass plates. As for method 2, sources of CO2 were from the liquid solution of Na2CO3 and gaseous CO2 above the liquid solution containing suspended particles of catalyst. Method 3 was similar to method 2 with addition of CuCl2 in the liquid solution of Na2CO3. The major product via methods 1 and 2 was methanol. An addition of CuCl2 to the solution containing suspended Cu/TiO2 catalyst can form CuCl/Cu/TiO2 which further catalytically enhanced the reduction of CO2 and CH3OH, producing CH4 and increasing its yield. The determining step for the production of methane is the additions of Na2CO3 and CuCl2 in the aqueous solution. The orders of concentrations of Na2CO3 enhancing the methane yields were 0.1 > 0.2 > 0.3 > 0.05 M Na2CO3 at 0.1 M CuCl2, while those of CuCl2 were 1 > 2 > 0.1 > 0 > 4 M CuCl2 at 0.1 M Na2CO3. The results obtained from this study are useful for better understanding the UV/photocatlyst process for the reuse of CO2. Method 4 was electrolysis using red copper electrode with power supply standards of 12 relative volts and 1 amp. The orders of concentrations of Na2CO3 enhancing the ethylene yields were 0.2 > 0.1 > 0.3 > 0.4 M Na2CO3 at 0.1 M CuCl2. As for the enhancing effects of concentrations of CuCl2 on the methane yields, the orders were 0.1 > 0.05 > 0 > 0.2 M CuCl2 at 0.2 M Na2CO3. The degradation efficiencies of gaseous CO2 was 88% and the products yielded of C2H4, CO, CH4, HCOOH, H2, and O2 were 53211, 74788, 3433, 15832, 80791 and 101642 μg at 0.2 M Na2CO3 and 0.1 M CuCl2. Method 5 was combining photocatalyst and electrolysis processes for the reduction of CO2. The yields of products of method 5 relative to those of method 4 decreased two-thirds for C2H4, CH4 and HCOOH, and half for CO. As for O2, the yields of method 5 and 4 were about the same. However, the yield of H2 of method 5 increased slightly as compared to that of method 4 with the addition of 0.5 g Cu/TiO2 catalyst at 0.2 M Na2CO3 and 0.1 M CuCl2. The result indicated that combining photocatalyst and electrolysis processes would restrain the reduction efficiency of CO2. The technology for the reduction of CO2 to useful chemicals elucidated by this study is environmentally favorable.
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