【作者】 秦士跃；

【导师】 辛峰；

【作者基本信息】 天津大学 ， 化学工程， 2013， 博士

【摘要】 随着世界经济的快速发展，大量使用化石燃料，大气中CO2浓度持续增加，CO2导致的环境问题引起人们的高度重视。如何减少大气中CO2含量、缓解“温室效应”已成为世界关注的热点。光催化还原CO2具有反应条件温和、对环境友好和利用太阳能等优点，利用CO2合成高附加值的化学品或燃料，可以实现CO2—化学品、燃料—CO2良性循环。本文研究在甲醇中光催化还原CO2制备甲酸甲酯，并利用在线衰减全反射傅里叶变换红外光谱（ATR-FTIR）法对其反应过程机理进行了研究，主要内容如下：第一，采用油酸作为表面活性剂，利用溶剂热合成法制备SrTiO3纳米颗粒，通过光催化还原的方法在SrTiO3表面负载Ag纳米颗粒，用于CO2在甲醇中光催化还原制备甲酸甲酯。研究了SrTiO3不同制备方式对光催化活性的影响，油酸作为表面活性剂溶剂热合成法制备的SrTiO3活性较高，油酸可以抑制SrTiO3纳米颗粒团聚，促进其分散。Ag颗粒负载可以扩展复合光催化剂的光谱响应范围，增加光能吸收和利用；可以作为电子阱促进电子-空穴分离，从而提高光催化活性。Ag负载量过高时Ag纳米颗粒长大并发生团聚，且催化剂裸露表面减少，影响光催化活性。第二，采用AgX（X=Cl，Br，I）作为光催化剂在甲醇中光催化还原CO2制备甲酸甲酯，并利用在线ATR-FTIR光谱法研究其反应过程。采用沉淀法制备AgCl、AgBr和AgI光催化剂，经重复利用实验和对反应前后催化剂进行XRD表征，催化剂活性比较稳定。跟踪反应过程溶液中CO2浓度变化，峰强度减少2.2%，CO2参与光催化反应；反应的中间产物有甲酸、甲醛，CO2被还原成甲酸，甲醇被氧化成甲醛，甲酸与甲醇发生酯化反应生成甲酸甲酯，甲醛二聚生成甲酸甲酯，甲酸甲酯主要通过酯化反应生成。第三，研究ZrO2纳米片制备及其在甲醇中光催化还原CO2制备甲酸甲酯。利用二乙烯三胺（DETA）作为溶剂制备的ZrO2(DETA)是纳米片组成的层状结构，焙烧后除去DETA并提高ZrO2结晶度，层状结构形貌保持不变，层间隙扩大。利用超声法，在异丙醇溶剂中进行层状ZrO2剥离，得到ZrO2纳米片。结晶度提高，有利于增加光催化活性；纳米片形貌结构有利于增大接受光照的面积，有利于晶体内部产生的电子和空穴向表面转移和促进电荷分离，从而提高光催化活性。第四，研究AgCl-ZrO2纳米片复合光催化剂的制备及其在甲醇中光催化还原CO2制备甲酸甲酯。制备层状ZrO2，利用超声法进行层状ZrO2剥离，得到ZrO2纳米片。在ZrO2纳米片上负载AgCl纳米颗粒，制备AgCl-ZrO2纳米片复合光催化剂。AgCl纳米颗粒负载在ZrO2纳米片表面且分散比较均匀，当AgCl负载量为40wt％时活性最高。AgCl纳米颗粒与ZrO2纳米片复合形成复合光催化剂，可以促进电子-空穴分离，提高光催化活性；AgCl负载量过高时纳米颗粒发生团聚影响光催化活性。更多还原

【Abstract】 With the development of the world economy the rapid increase in the level ofcarbon dioxide is a matter of great concern. The atmospheric carbon dioxideconcentration will continue to increase due to the fossil fuel consumption. How toreduce CO2in the atmosphere to ease the “greenhouse effect” has become the focus ofthe world attention. A possible avenue for the sustainable development is to use thephotocatalysts for conversing CO2into hydrocarbons with the help of solar energy.Photocatalytic reduction of CO2is under mild reaction conditions, environmentalfriendly and can use solar energy. The use of CO2to synthesis high-value-addedchemicals or fuel can achieve the CO2-chemicals, fuel-CO2circle. In this paper,photocatalytic reduction of CO2in methanol to prepare methyl formate and theirmechanistic studies by on-line ATR-FTIR spectroscopy was investigated. The maincontents were as follows:Firstly, SrTiO3were synthesized by solvothermal method using oleic acid assurfactant, and Ag nanoparticles were loaded on the SrTiO3surface through thephotoreduction method. SrTiO3prepared by using oleic acid as surfactant showed thehigher activity owing to the smaller size and well dispersion. The Ag nanoparticlescan extend the spectral response from UV to visible area and increase light absorption.Ag nanoparticles can be used as electron traps for electron-hole separation, therebyenhancing the photocatalytic activity; however too much Ag loading could cause theformation of large nanoparticles and agglomeration, which was detrimental to thephotocatalysis.Secondly, silver halides were used for the CO2photoreduction, and on lineATR-FTIR spectroscopy was used to study the reaction process. The photocatalysts ofsliver halides were stable under repeated application since no siginificant decrease inthe photocatalytic reaction rate. The XRD patterns of the as-prepared silver halidesand silver halides used after5consecutive photocatalytic reactions showed thecatalysts were relatively stable. After6h of the reaction the CO2peak intensity wasreduced by2.2%, which indicated that CO2was consumed in the photoreaction. Theintermediates such as formic acid and formaldehyde were monitored in the solution.Formic acid was the2-electron reduction product of CO2, and formaldhyde was theprimary oxidation product of methanol. The methyl formate could be producedthrough the esterification of formic acid and methanol, dimerization of formaldehydevia Tishchenko reaction, but mainly through the esterification reaction.Thirdly, ZrO2nanosheets were synthesized by a two-step method and used forthe CO2photoreduction. Layered ZrO2was prepared by the solvothermal method indiethylenetriamine. After calcination DETA was removed and the crystallinity of ZrO2 was improved. The morphology of layered structure was remained and the gapbetween the layers was enlarged. Layered ZrO2was exfoliated to ZrO2nanosheets inisopropanol under ultrasonic treatment. The high degree of crystallinity helped toincrease the photocatalytic activity; ZrO2nanosheets favored for transfering electronsand holes to the surface, which enhanced the photocatalytic activity.Fourthly, the composite photocatalysts of AgCl-ZrO2nanosheets weresynthesized by anchoring AgCl nanocrystals on the surface of ZrO2nanosheets andused for the CO2photoreduction. The heterogeneous precipitation process ofAg+-ZrO2nanosheets suspension with chloride added dropwise was used tosynthesize AgCl-ZrO2nanosheets composites. The optimal composite with40wt%AgCl showed the higher photocatalytic activity. The enhanced photocatalytic activityinduced by the AgCl loading was attributed to the interfacial transfer ofphotogenerated electrons and holes between AgCl and ZrO2nanosheets, which leadsto effective charge separation. High AgCl loading amounts caused agglomeration,which decreased the photocatalytic activity.更多还原