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CO2光还原催化剂的制备及反应微观机理研究
杜云舒
学位类型硕士
导师邱恒山
2017-05-28
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
关键词二氧化碳 光还原 氧化锌 二氧化钛 体相氢 微观机理
其他摘要

CO2是造成温室效应的主要人为温室气体之一。然而,随着煤炭、石油化工产业的快速发展,CO2的大量排放成为一个无法回避的问题。如何实现CO2的有效去除和转化将成为一个有着重要科学和现实意义的课题。光催化技术以其成本低廉、绿色环保且可持续发展等优点成为去除CO2最有前景的技术之一。本论文以可控制备的ZnO和TiO2纳米颗粒为基础,通过原位光催化表征系统探讨了光催化效率的影响因素,并结合真空原位红外光谱的方法实现了对吸附脱附行为和光催化反应微观过程的研究。主要研究内容包括:1、探究了样品制备方法对CO2光还原实验的影响因素。实验中我们发现有些阴离子和有机成分具有一定的光分解性质,并会影响到后期的光催化效率表征实验结果;另外,在材料合成过程中引入还原性较强的阳离子(如提供碱性环境),则有可能在后期的CO2光还原实验中形成较强的碳酸盐,从而在一定程度上造成催化剂的失活。2、利用原位光催化表征系统和真空原位红外光谱系统对ZnO基CO2光还原的反应过程进行检测,发现CO2还原的初步还原产物为CO,并且水蒸汽环境有利于CO2的光还原反应的进行。同时,探究了CO2光还原反应的温度特性,发现在303-393 K之间,CO的生成速率基本不随温度的改变而发生变化,说明CO2的光还原反应的速控步骤不是发生在催化剂表面的CO2吸附和还原过程,而有可能是受温度影响不大的光激发过程。3、初步探索了氢原子在ZnO体相中的形成和扩散行为。这是由于,一方面氢原子在ZnO体相的存在有一定的普遍性;另一方面,ZnO体相氢的存在会对ZnO表面的CO2吸附和光催化过程产生影响。实验中我们发现暴露于ZnO表面的氢原子(或氢分子)倾向于扩散到ZnO的体相中形成电子掺杂效应。通过真空退火,高温氧化和常温吸附CO2的方式可以促进氢在ZnO体相中的向外扩散,从而在一定程度上可以实现对体相氢浓度的控制。4、初步研究了在锐钛矿TiO2表面CO2光还原的过程。实验中我们发现,一定量的H2O的存在有利于CO2光还原的进行,然而过多的H2O反而会抑制反应的进行,这是由于H2O和CO2的竞争吸附所致,H2的存在则部分改变了反应路径例如部分CO2发生加氢反应。

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CO2 is primary man-made greenhouse gas among those gases which cause greenhouse effect. However, with the rapid development of coal, petroleum, and chemical industry, large amounts of CO2 emission become an unavoidable problem. How to realize effective removal and conversion of CO2 will become a research topic with important scientific and practical significance. Photocatalytic techniques are low-cost, pollutionfree, and sustainable, which makes the photocatalytic removal of CO2 one of the most promising techniques.In this thesis, based on the controllable synthesis of ZnO and TiO2 nanoparticles, we have studied the influence factors of photocatalytic efficiency by a mass spectrometer-based photocatalytic characterization system combined with an in situ Fourier Transform Infrared Spectroscopy system, including adsorption, desorption and photocatalytic reaction process. The main research contents are summarized as following:1. We explored the influence of preparation method on photocatalytic reduction efficiency of CO2. In experiments we found that the majority of anions and organic components have the properties of photo-induced decomposition, which could affect the characterization results of photocatalytic efficiency. In addition, in the process of materials synthesis if strong reductive cation is introduced, (e.g., providing the basic environment) it could generate stronger carbonate in photocatalytic CO2 reduction experiments, which will caused the deactivation of the catalyst.2. We monitored the photoreduction of CO2 on ZnO nanoparticles by mass spectrometer-based photocatalytic characterization system and in situ Fourier transform infrared spectroscopy. The initial production of CO2 reduction is CO, and steam environment promotes this process. We explored the temperature effect on the photoreduction of CO2, even though the temperature is vared from 303 K to 393 K, the generating rate of CO is remain unchanged. This suggests that rate-determining step of this reaction is not the steps that CO2 adsorption in the catalyst surface and reduction process, but light stimulating separation of electron-hole which is not effected by the temperature in photocatalytic reaction.3. We explored the formation and diffusion behavior of hydrogen atoms in the ZnO bulk phase. This is because, on the one hand, the existence of the hydrogen atoms in the ZnO bulk phase has a certain universality, and on the other hand, the existence of hydrogen have influences on CO2 adsorption and catalytic process on the surface of ZnO. In experiments we found hydrogen atoms (hydrogen molecules) on the surface of ZnO tended to diffuse to the bulk phase of ZnO and form electronic doping effect. Vacuum annealing, oxidation at high temperature and adsorption CO2 at room temperature can promote out diffusion of hydrogen in ZnO bulk phase, thus to some extent, we can control the concentration of bulk hydrogen in ZnO.4. We discussed the photoreduction of CO2 on TiO2 nanoparticles. A certain amount of water and hydrogen will promote this reaction, while they can inhibit it when they are superfluous, this is because the competitive adsorption of H2O and CO2. In the presence of hydrogrn, the path of the reaction are changed, such as the hydrogenation reaction of CO2.

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4978
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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杜云舒. CO2光还原催化剂的制备及反应微观机理研究[D]. 北京. 中国科学院大学,2017.
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