利用TiO_2/SO_4^(2-)光触媒催化还原CO_2之参数影响与反应路径探讨

Parameter Effects and Reaction Pathways of Photoreduction of CO_2 over TiO_2/SO_4^(2-) Photocatalyst

将改良式溶胶-凝胶法制备的酸性触媒TiO2/SO24-涂布于不锈钢网上,并利用自行设计之批次式光催化反应器,在三组近紫外灯管(波长为365nm,光强度为2.0mW/cm2)照射下,进行CO2光催化还原反应操作参数(还原剂种类、CO2初始浓度和反应温度)之影响研究.结果显示,使用氢气为还原剂可获得最高的光催化还原速率,光还原反应之主要气态产物为CO和甲烷,其次为微量的乙烯与乙烷.同时,光催化还原速率亦随着CO2初始浓度及反应温度的提高而增加.FT-IR光谱分析发现,TiO2/SO42-光触媒表面有甲酸、甲醇、碳酸盐、甲酸盐及甲酸甲酯等产物之存在.TiO2/SO42-光触媒催化还原CO2有两种可能反应路径,其中一种反应路径生成CO,CH4,C2H4及C2H6等气态产物;而另一种反应路径则生成CO23a-ds,CH3OHads,HCOOa-ds,HCOOHads,HCOHads与HCOOCH3ads等吸附在光触媒表面的产物.

The feasibility of applying a modified acidic photocatalyst （TiO2/SO4^2- ） to reduce carbon dioxide was investigated. The photocatalytic reduction of CO2 was conducted in a bench-scale batch photocatalytic reactor. Three near-UV black lamps with a maximal spectrum wavelength of 365 nm were assembled on the top of the reactor to provide an average irradiated light intensity of 2.0 mW/cm^2. The TiO2/SO4^2- photocatalyst was prepared by a modified sol-gel process and coated on stainless steel substrates for the reduction of CO2. Experimental parameters such as the reductants, the initial CO2 concentration, and the reaction temperature were investigated. The results indicated that the highest photoreduction rate of CO2 was observed using H2 as a reductant over TiO2/SO4^2- . The major gaseous products from CO2 photoreduction were carbon monoxide and methane, while other minor products of ethene and ethane were also detected in the experiments. The photoreduction rate of CO2 was found to be increased with initial CO2 concentration and reaction temperature, which promoted the formation of reaction products. Furthermore, the FT-IR spectra showed that formic acid, methanol, carbonate ions, formaldehyde, and methyl formate formed on the surface of TiO2/SO4^2- photocatalyst. Two reaction pathways of CO2 photoreduction over TiO2/SO4^2- photocatalyst were proposed. One reaction pathway described the formation of gaseous products CO, CH4, C2H4, and C2H6. The other reaction pathway formed CO3ads^2-, CH3OHads, HCOOads^-, HCOOHads, HCOHads, and HCOOCH3ads on the surface of TiO2/SO4^2- photocatalyst.