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CeO2/TiO2的制备及其光催化还原CO2的研究
王云
学位类型硕士
导师李希友
2016-05-24
学位授予单位中国科学院大学
学位授予地点北京
学位专业材料工程
关键词Tio2 Ceo2 水热法 金红石 Ce3++ Co2光催化还原
摘要

随着工业的快速发展,排放到大气中的CO2总量逐年增加,进而导致温室效应增强和全球气温变暖。因此,从根源上减少CO2的排放及实现其资源化成为亟待解决的全球性问题。通过太阳能激发半导体光催化材料,产生光生电子?空穴,诱发氧化?还原反应,可将CO2与水转化成碳氢燃料或其它化学品。该过程常温常压下进行,直接利用太阳能无需耗费辅助能源,被认为是理想的CO2转化方法。但目前光催化还原CO2效率还很低。光催化剂的设计与合成是解决效率问题的关键。半导体TiO2因其无毒、化学性质稳定、强的氧化还原能力、成本低等优点,成为研究最广泛、最深入的半导体材料之一。但是,TiO2光催化还原CO2的发展受三种重要因素制约,即光响应局限于仅占太阳光总能量~4%的紫外光、有限的光量子产率和TiO2与CO2之间较弱相互作用。人们对前两者进行了大量研究,通过染料敏化,金属和非金属离子掺杂,异质结、缺陷等方法,发展出许多光响应范围宽和光量子产率有所提高的钛基光催化材料。然而,对后者的关注相对较少。本研究构建了碱性CeO2与TiO2的复合光催化剂,通过CeO2增强催化剂表面对CO2分子的吸附、活化剂光学性质,进而改善光催化还原CO2的效能,具体研究内容如下: (1)采用二(2-羟基丙酸)二氢氧化二铵合钛(TALH)和硝酸铈为原料,通过一步水热法制备了高分散CeO2/TiO2,系统表征了其形貌、结构、光学特性及光催化还原CO2的活性。利用吸附量热法和原位红外技术,研究了CO2分子在催化剂表面的吸附和光催化还原CO2的反应微观过程。结果表明,高分散CeO2/TiO2增强了对CO2分子的吸附,其在样品表面主要存在三种吸附态:单配位碳酸根(m-CO32?)、双配位碳酸根(b-CO32?)和双配位碳酸氢根(b-HCO3?)物种。CeO2增加了表面吸附物种b-CO32?和b-HCO3?的生成,而它们在模拟太阳光辐射下更容易转化成活性中间产物CO2?另外,CeO2与TiO2形。成异质结,促进了光生电子-空穴的分离。CeO2/TiO2光催化还原CO2的活性显著高于单组分,这种归因于CeO2对CO2表面物种的调节以及光生载流子分离效率的提高。 (2)通过浸渍法制备了CeO2修饰的锐钛矿、板钛矿、金红石光催化材料,利用BET、紫外-可见漫反射及稳态荧光光谱、CO2-TPD等,研究其织构、结构、光学性质及CO2与催化剂表面的相互作用。研究表明,含Ce3+的CeO2增强了材料的可见光吸收、光生电子-空穴对的分离效率和对CO2分子的捕获,促使复合组分光催化还原CO2活性比单组分TiO2的高。XRD和显微拉曼光谱分析表明,CeO2与金红石相TiO2之间发生了强相互作用,导致金红石中产生了的Ti缺陷。这解释了CeO2/金红石光生电荷分离效率和光催化活性的提高程度明显高于相应的CeO2/锐钛矿和CeO2/板钛矿。CeO2/金红石光催化还原CO2产生CO的量比纯金红石高出了近3倍。 (3)以TALH和乙酸铈为原料,采用浸渍法,并通过不同气氛下(氧气和氩气)热处理,获得了不同Ce3+含量的CeO2/TiO2复合样品。各种表征结果表明,材料具有介孔结构,孔径分布较均匀,对可见光有较强的可见光吸收,光生电子空穴分离效率明显比单组分TiO2明显提高。Ce3+的含量对甲烷的选择性有明显影响。在惰性氛(Ar)下处理的CeO2/TiO2光催化表面的Ce3+含量最高,达62.2%,其光催化CO2产CH4的量是TiO2样品近4倍,是CeO2/TiO2(O2)的2倍。

其他摘要

Along with the rapid development of industry, environment have been suffered from broken severitly. The amount of CO2 gradually increased and resulted "greenhouse effect" serious and the global warming. Therefore, the reduction of CO2 emission has been the global problem. The semiconductor photocatalysts after solar light irradiated can generate photoproduced electron-hole, and CO2 and H2O can be transformed to induced value-added hydrocarbon fuels. This process can directly used solar light and reaction condition mild, was regarded as the most promising method of CO2 transformation. However, the transformation efficiency of CO2 photoreduction is still very low. The selection and fabrication of photocatalysts are the important content of the research of CO2 photocatalytic reduction. Titanium dioxide (TiO2) has attracted much attention because of its specific properties: nontoxicity, chemical stability, redoxi properties, and low cost. However, its wide band gap (3.2 eV) makes it capture only 5% of solar energy, rapid recombination of photoinduce electron-hole and the weak interaction between CO2 molecular and TiO2 surface limited the application of TiO2. The former two limitations have been extensively studied by means of metal coupling, heterogeneous building, dye sensitization or nonmetal doping. However, the studies of later are a few. We structured CeO2/TiO2 photocatalysts, the extence of CeO2 can strength CO2 adsorption, activate optical property, and enhance the activity of CO2 photoreduction. The specific contents are as following: (1) Highly dispersed CeO2/TiO2 were synthesized by one-pot hydrothermal method and its morphology, structure, opotical properties, and activities for CO2 photoreduction were explored. Microcalorimetric measurement and in-situ infrared spectroscopy were used to reveal the strengths and states of CO2 adsorption and the involved photoreduction course of CO2 with H2O vapor. Monodentated carbonate (m-CO32-), bidentated carbonate (b-CO32?)and bidentated bicarbonate (b-HCO3-)are found to be the main surface species for the coadsorption of CO2 and H2O on catalyst surfaces. The presence of CeO2 containing Ce3+ strengthens the bonding of CO2 with catalyst surfaces and increases the production of b-CO32?and b-HCO3? species. Unlike m-CO32?, b-CO32? and b-HCO3? surface species could be readily transformed to surface CO2? under simulated sunlight irradiation. In addition, the presence of CeO2 containing Ce3+ facilitates photo-generated charge separation. As a result, ceria-tuned CO2 adsorption and enhanced charge separation are jointly responsible for the increased activity of CeO2/TiO2 catalysts. (2) CeO2 modified anatase, brookite and rutile were synthesized by impregnation method, and its structure, optical properties, and activities for CO2 photoreduction were explored. The presence of CeO2 containing Ce3+ can extend the light response range of samples, facilitate photo-generated charge separation and enhance the adsorption of CO2. CeO2/TiO2 catalysts have a higher photocatalytic activities than pure TiO2 or CeO2. XRD and Raman results indicated the defects of titanium were generated in R-TiCe, because of strong interaction between CeO2 and rutile. Higher CO2 photo-reduction activities of R-TiCe sample was attributed to the generation of titanium defects, and CO generated amount of R-TiCe is about 3 times in CO2 photoreduction compared with R-Ti. (3) CeO2/TiO2 composites were synthesized by impregnation method using TALH and cerium acetate as precursors. TiCe(O2) and TiCe(Ar) samples with different Ce3+ content were obtained by treated CeO2/TiO2 composites under O2 and Ar atmosphere respectivitely. TiCe(O2) and TiCe(Ar) samples had mesoporoud structure, uniform pore size, strengthed visible light adsorption, and enhanced photo-induced carriers separation efficiency. Ce3+ amount of TiCe(Ar) samples as large as 62.2%.We studied the activities for CO2 photoreduction of TiO2 and CeO2 modified TiO2 under simulative solar light in 6 h. The result showed that Ce3+ amount is influence on the selectivity of CH4 generation, and CH4 generated amount of TiCe(Ar) is about 4 times and 2 times in CO2 photoreduction compared with TiO2 and TiCe(O2) respectively.

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4575
专题环境科学与技术研究室
作者单位中国科学院新疆理化技术研究所
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王云. CeO2/TiO2的制备及其光催化还原CO2的研究[D]. 北京. 中国科学院大学,2016.
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