铈基催化剂表界面特性及其在催化氧化甲醛中的作用

SURFACE AND INTERFACE CHARACTERISTICS OF CERIUM-BASED CATALYST AND ITS ROLE IN CATALYTIC OXIDATION OF FORMALDEHYDE

姜桂敏

11849262

硕士

化学工程领域工程

张作泰

2020-05-26

2020-07-20

哈尔滨工业大学

深圳

室内空气污染与人类日常生活密切相关，甲醛作为主要的室内污染物，会对人体的健康造成巨大的伤害，因此如何高效环保的治理室内甲醛问题成为了人们关注的环境问题之一。贵金属催化剂因其对甲醛氧化反应具有良好的活性，可在低温下进行甲醛转化，且反应仅产生无毒无害的二氧化碳和水，受到人们的广泛关注。贵金属与载体之间的界面效应对其催化氧化活性起到重要作用，本文主要研究贵金属银和钯与二氧化铈载体的表界面效应及其在甲醛氧化中的作用。选择商用CeO2和CeO2纳米棒作为载体，通过沉淀沉积法合成的Ag/CeO2催化剂，并对其进行甲醛催化氧化活性测试。反应性测试结果表明Ag负载CeO2纳米棒催化剂具有高的催化活性，在空速为36000 mL/(g·h)，80 ℃下即可将220 ppm的甲醛完全转化。实验结果表明，与暴露（111）晶面的商用CeO2相比，暴露（110）和（100）晶面的CeO2纳米棒具有大量氧空位，随着Ag的加入，可进一步促进二氧化铈氧空位的增加。Ag与CeO2纳米棒暴露晶面之间的强相互作用极大地促进了表面活性氧活动性。原位红外光谱研究表明二氧化铈上的氧空位促进了HCHO的吸附，并且生成的为甲酸盐。此外，Ag的存在促进了HCHO向甲酸盐的进一步转化，以及甲酸盐向最终产物的转化。通过沉淀沉积法将Pd负载在商用CeO2，CeO2纳米棒和CeO2纳米立方体上，对Pd/CeO2催化剂活性测试发现，在氢气还原预处理后，催化剂的活性有巨大提升。其中Pd负载在CeO2立方体上的催化剂具有最高的催化活性，可在空速为36000 mL/(g·h)，24 ℃下即可将220 ppm的甲醛完全转化。通过对催化剂进行表征发现， CeO2立方体可通过与Pd的界面作用维持其金属态。原位红外光谱结果表明Pd/CeO2催化剂在24 ℃下，HCHO吸附产生的中间体不仅有DOM和甲酸盐，还有一定量的CO。这说明HCHO在Pd/CeO2催化剂上氧化有另一条反应路径，CO的生成更有利于甲醛在Pd/CeO2催化剂上的氧化。

Indoor air pollution is closely related to human daily life. Formaldehyde, as the main indoor pollutant, will cause huge harm to human health. Therefore, how to efficiently and environmentally manage indoor formaldehyde has become one of the environmental issues that people are concerned about. The noble metal catalyst has high activity on the oxidation reaction of formaldehyde. It can carry out formaldehyde conversion at low temperature, and the reaction only produces non-toxic and harmless carbon dioxide and water, which has attracted widespread attention. The interface effect between the noble metal and the support plays an important role in its catalytic oxidation activity. This article mainly studies the surface interface effect of the precious metal silver and palladium with the ceria support and its role in the oxidation of formaldehyde.The commercial CeO2 and CeO2 nanorods were selected as supports, and the Ag/CeO2 catalyst synthesized by the precipitation deposition method was tested for its formaldehyde catalytic oxidation activity. The reactivity test results showed that the Ag/CeO2 catalyst with CeO2 nanorods as support had high catalytic activity, and 220 ppm of formaldehyde could be oxidized at 80 ℃, while space velocity was 36000 mL/(g·h). Compared to commercial CeO2 with exposed (111) plane, the characterization results show that CeO2 nanorods have a large amount of oxygen vacancies with exposed (110) and (100) plane. With the addition of Ag, it can further promote the increase of oxygen vacancies in CeO2. The strong interaction between Ag and CeO2 nanorod greatly promotes the formation of surface active oxygen and the ability to release oxygen. In situ diffuse reflectance infrared fourier transform (in situ DRIFT) spectroscopy showed that oxygen vacancies on CeO2 promoted the adsorption of HCHO, and the main intermediate product was formate. In addition, the presence of Ag promotes the further conversion of HCHO to formate and the conversion of formate to final products.Pd was supported on commercial CeO2, CeO2 nanorod and CeO2 nanocube by precipitation deposition method. The activity test of Pd/CeO2 catalyst found that the activity of the catalyst has been greatly improved after hydrogen reduction pretreatment. Among them, the Pd/CeO2 catalyst supported on CeO2 nanocube has the highest catalytic activity, and the formaldehyde can be converted to CO2 and H2O at 24 ℃ completely, while space velocity was 36000 mL/(g·h). Through characterizations of the catalyst, it was found that CeO2 nanocube can maintain the metallic Pd through the interface interaction. The results of in situ DRIFT spectroscopy showed that at 24 ℃, the intermediates produced by HCHO adsorption on Pd/CeO2 catalyst include not only dioxymethylene and formate, but also a certain amount of CO. This shows that there is another reaction path for HCHO oxidation on Pd/CeO2 catalyst and the formation of CO is more conducive to the oxidation of formaldehyde on the Pd/CeO2 catalyst.

界面效应 氧空位 二氧化铈 贵金属 甲醛氧化 反应机理

interface effect oxygen vacancies cerium oxide noble metal reaction mechanism

中文

联合培养

南方科技大学

姜桂敏. 铈基催化剂表界面特性及其在催化氧化甲醛中的作用[D]. 深圳. 哈尔滨工业大学,2020.