光催化选择性转化多元醇合成高附加值产物

PHOTOCATALYTIC SELECTIVE CONVERSION OF POLYOLS TO VALUE-ADDED PRODUCTS

雷烨琛

11749171

硕士

材料工程

邓永红

2019-06-01

2019-06-28

哈尔滨工业大学

深圳

多元醇主要来源于天然产物及生物柴油制作过程中的副产品，是一种廉价的工业原料。但是由于技术限制，这些多元醇副产品无法得到有效的利用，造成大量资源浪费。因此，开发一种技术，将这些价格低廉的多元醇转化成高附加值的产品，具有重要的意义。论文利用甘油作为多元醇模型分子，探究了贵金属负载型TiO2催化剂的性能及反应条件对光催化转化多元醇反应产物及途径的作用机制，其结论对后续多元醇的光催化氧化研究具有一定的理论指导意义。本课题结合透射电子显微镜（TEM）、X射线光电子能谱（XPS）、核磁共振定量氢谱（H-NMR）、原位红外光谱与质谱联用的技术（in-situ FTIR-QMS）、电感耦合等离子体放射光谱仪（ICP-AES）分析了在无氧和有氧条件下，光催化甘油转化的反应机理和决速步，以及光催化助剂的种类对该反应的影响。同时还结合了原位X射线光电子能谱和碘滴定检测中间产物及自由基活性，对该反应机理进行了进一步验证。现将研究结果总结如下：1. 在无氧条件下，结合了in-situ FTIR-QMS、H-NMR以及in-situ XPS，探究了1 wt% Pt/TiO2、1 wt% Pd/TiO2、1wt% Au/TiO2这三种催化剂在紫外光照射的条件下，对光催化甘油氧化过程的影响。实验结果表明，甘油在纯TiO2的作用下，基本不发生反应。TiO2上负载的贵金属纳米颗粒有助于促进甘油光催化转化反应的决速步，即表面吸附态H原子的脱附这一过程，从而促进甘油转化。反应过程中，首先发生的是-OH中H原子的脱附过程，形成酮，随后C-C键断裂，生成含有两个碳和一个碳的产物，产物有甲酸、甲醛、1,3-二羟基丙酮（DHA）、乙酸、羟基丙酮和乙醛酸这六种。其中负载Pd纳米颗粒的催化剂对甘油的催化转化效果最好，期望产物DHA的选择性最高。2. 在空气条件下，结合in-situ FTIR-QMS、H-NMR以及in-situ UV-vis探究了负载贵金属的TiO2催化剂光催化甘油氧化的过程。发现1 wt% Au/TiO2对甘油的光催化转化的作用效果最好，对DHA的选择性最高。实验结果表明，甘油在纯TiO2的作用下，会发生氧化反应，但效果不明显。而Pd和Pt纳米颗粒修饰的TiO2将会导致甘油产物完全氧化。经in-situ FTIR-QMS等表征测试发现，有氧条件下，光催化转化甘油反应的决定步骤是光生吸附态H+与O2(·O2-)发生反应，生成H2O，从而使吸附态H+从催化剂表面脱附。而Pd/TiO2与Pt/TiO2这两种光催化剂，由于倾向于使甘油的C-C键裂解以及完全氧化，从而使反应生成的产物大部分被彻底氧化产生了CO2。

Polyols are mainly derived from natural products and by-products of the biodiesel production, and thus the price of polyols is usually very low. Due to technical limitations, these by-products cannot be effectively utilized, thus resulting in lots of waste. Therefore, it is important to develop a green approach to convert these cheap polyols into value-added products. In my thesis, glycerol was used as a model polyol to explore the performance of metal decorated TiO2 photocatalysts and the photocatalytic reaction pathways of polyol conversion into value-added products under different reaction conditions. And the conclusions can be considered as a fundamental theory to explore photocatalytic conversion of other polyols. A series of characterization methods, such as transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), proton nuclear magnetic resonance (H-NMR) and in-situ Fourier-transform infrared spectroscopy- quadrupole mass analyzer (in-situ FTIR-QMS) were used to analyze the properties and performances of the photocatalysts, as well as the reaction mechanisms of photocatalytic glycerol conversion under anaerobic and aerobic conditions. In-situ XPS and iodine titration have been employed to detect the possible reaction intermediates and free radical activity to verify the reaction mechanisms. The results of the thesis are summarized as the following: I. Under anaerobic conditions, the effect of metal identity on photocatalytic oxidation of glycerol under UV light irradiation was investigated by combining in situ FTIR-QMS, H-NMR and in-situ XPS. It is found that glycerol does not react with pure TiO2, and the catalyst loaded with metal NPs can accelerate the oxidation process of glycerol. The first step of the reaction is the desorption process of H atoms in -OH group, forming ketone. And then the C-C bond is broken to form products containing two carbons or one carbon. The products of the reaction are formic acid, formaldehyde, and 1,3-dihydroxyacetone (DHA), acetic acid, hydroxyacetone and glyoxylic acid. The results show that Pd/TiO2 presents the optimum catalytic activity among the three catalysts with a higher selectivity towards desired product of 1,3-Dihydroxyacetone (DHA). The metal NPs accelerate the photocatalytic conversion rate of glycerol by means of promoting the desorption of surface-adsorbed H atoms. II. With the presence of oxygen, the catalytic activity of glycerol oxidation by noble metal supported TiO2 photocatalysts was investigated by H-NMR, in-situ FTIR-QMS and in-situ UV-vis. It is found that 1 wt% Au/TiO2 presents the best effect on the photocatalytic conversion of glycerol under aerobic conditions with the highest selectivity to DHA. The results indicate that the strong oxidation power of Pd and Pt NPs on TiO2 resulting in complete oxidation of glycerol. It is found that the photo-induced adsorbed H+ reacting with O2 (·O2-) is the initial step during the photocatalytic conversion of glycerol, resulting in the formation of H2O. Then the adsorbed H+ is desorbed from the catalyst surface. The two photocatalysts, Pd/TiO2 and Pt/TiO2, have the tendency to cleave and completely oxidize the C-C bond of glycerol, resulting in the formation of CO2.

光催化 多元醇转化 甘油 贵金属纳米颗粒 反应机理

photocatalysis polyol conversion glycerin noble metal nanoparticles reaction mechanism

中文

联合培养

南方科技大学

雷烨琛. 光催化选择性转化多元醇合成高附加值产物[D]. 深圳. 哈尔滨工业大学,2019.