Pd基催化剂上催化氧化邻-二甲苯研究
文献类型：学位论文
| 作者 | 王亚飞 |
| 学位类别 | 博士 |
| 答辩日期 | 2014-05 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 贺泓 |
| 关键词 | 催化氧化，邻-二甲苯，钯基催化剂，有序介孔，铈锆复合氧化物，Catalytic oxidation, o-Xylene, Palladium catalysts, Ordered mesoporous, Zirconium-cerium mixed oxide |
| 其他题名 | Catalytic Oxidation of o-Xylene over Supported Pd Catalysts |
| 学位专业 | 环境科学 |
| 中文摘要 | 挥发性有机物(VOCs)是大气污染物的重要成分，对大气环境和人体健康有严重危害，其中苯系物(苯、甲苯、二甲苯等)由于毒性大、难降解受到了广泛的关注。催化氧化是目前最具实用潜质的 VOCs控制技术，贵金属Pd由于具有较好的低温活性和选择性是最常用的催化剂活性组分之一。大量的研究关注了Pd物种在催化氧化VOCs中的作用，但何种价态的Pd是催化反应的活性中心一直存在争议，金属-载体间相互作用也尚不明确。 本文中首先采用沉淀法和硬模板法分别制备了颗粒状 Co3O4(B)和三维有序介孔Co3O4(3D)载体，并采用后浸渍法制备了 Pd/Co3O4(BL)和Pd/Co3O4(3DL)催化剂，发现三维介孔结构的引入，促进了 PdO在载体表面的分散，提高了催化剂的性能，260˚C时可将邻-二甲苯完全转化.采用原位负载法制备了3D结构更为规整有序的Pd/Co3O4(3D)催化剂，发现其催化性能非常优异，200˚C时即可将邻-二甲苯完全转化。H2-TPR和XAFS表征结果表明，PdO在Pd/Co3O4(3D)催化剂上是以高度分散的状态存在。说明有序的3D结构对 Pd/Co3O4催化氧化性能有重要的促进作用。 采用沉淀法和硬模板法分别制备了非介孔的 CeO2(B)和有序介孔的 CeO2(3D)，发现 CeO2(3D)同样具有比 CeO2(B)催化剂更好的活性。但原位负载了 Pd后，Pd/CeO2(3D)的催化活性并未明显提高，H2-TPR和 XPS表征结果表明，Pd物种与 CeO2(3D)载体之间产生较强的相互作用，并且形成了不利于催化反应进行的含 Pd新物种。非介孔Pd/CeO2(B)的催化剂活性较 CeO2(B)有明显提高归因于载体表面高度分散的 Pd活性物种。 采用浸渍法制备了一系列的 PdO/MOx（MOx=TiO2，Al2O3，SiO2，MnO2，CeO2，Co3O4）催化剂，并采用 H2和 NaBH4还原分别制备了载有还原态 Pd物种的Pd/MOx-H2和 Pd/MOx-NaBH4催化剂，发现170oC时，Pd/MOx-NaBH4催化剂对邻-二甲苯的去除率达到了 100%，而 PdO/MOx的去除率均低于 20%。Pd/MOx-H2催化剂中，MOx=TiO2，Al2O3，SiO2，CeO2时，其催化性能均较PdO/MOx有明显提高。而 Pd/MnO2-H2和Pd/Co3O4-H2催化剂，由于还原过程中氢溢流作用导致了Co3O4和MnO2载体的还原，出现了低价态的 Mn2O3、MnO、CoO和 Co单质等物种，破坏了催化剂的催化性能。因此，在还原预处理对载体没有产生影响的催化剂上，还原预处理制备的金属态Pd能够有效的提高 Pd基催化剂低温催化氧化邻二甲苯活性；NaBH4还原较为温和，是一种更适合制备高活性 Pd基催化剂的预处理方法。 采用尿素均匀共沉淀法制备了不同 Zr添加量的Ce1-xZrxOy（x = 0.1, 0.3, 0.5）复合氧化物，并采用浸渍法和 NaBH4还原法制备了PdO/Ce1-xZrxO2和Pd/Ce1-xZrxO2-NaBH4催化剂。发现Pd/Ce1-xZrxO2-NaBH4的催化活性明显高于PdO/Ce1-xZrxO2催化剂，再次证明了还原预处理制备的金属态的 Pd是催化氧化反应的活性位点。Pd/Ce0.9Zr0.1O2-NaBH4（x= 0.1）催化剂具有最好的催化活性，150 oC时即将邻-二甲苯完全转化，归因于其较多的表面活性氧物种和 Pd的高度分散。 |
| 英文摘要 | BTX (Benzene, Toluene, and Xylene) form one of the major classes of VOCs in air on a large scale. BTX are of particular concern due to their destruction of environment and high toxic potential for human beings. The supported Pd catalysts have high activity for the catalytic oxidation of VOCs. The catalytic oxidation of BTX has also been widely studied over supported Pd catalysts. The performance of Pd-based catalysts for BTX deep oxidation has been reported to be dependent on many factors. Although the Pd state has been investigated by several researchers, the effect of the state of Pd on the catalytic VOCs still remains controversial. And the influence of the interaction between Pd and supports on catalytic oxidation was also not clear. In this study, ordered mesoporous Co3O4 (3D) and the bulk counterpart Co3O4 (B)were prepared by a nanocasting route and precipitation method, respectively. Pd was next loaded on both materials by an impregnation method (Namely Pd/Co3O4(3DL) and Pd/Co3O4(BL)). In addition, Pd/Co3O4(3D) was prepared by an in situ nanocasting method. All catalysts were tested for the total oxidation of o-xylene. As for Pd-loaded samples, Pd/Co3O4(3D) had much higher activity than Pd/Co3O4(3DL) and Pd/Co3O4(BL), with 100% conversion of o-xylene by oxidation at 200 ˚C. The characterization results show that the Pd/Co3O4(3D) catalyst synthesized by in situ nanocasting presented much more dispersed PdO species than the Pd/Co3O4(3DL) and Pd/Co3O4(BL) catalysts. The excellent catalytic performance of Pd/Co3O4(3D) is also attributed to its uniform mesostructure. Mesoporous CeO2(3D) and bulk CeO2(B) supports were prepared by nanocasting and precipitation, respectively. The mesoporous CeO2(3D) showed better activity than the bulk CeO2(B). Then Pd species was loaded on the supports by two methods (in situ nanocasting and co- precipitation). Pd/CeO2(B) showed much better activity than Pd/CeO2(3D). The greater quantity of exposed Pd species on bulk CeO2(B) played the major role in their better activity. The loss of active sites led to worse activity for Pd/CeO2(3D), which was caused by the stronger interaction between Pd and CeO2(3D). We prepared PdO/MOx catalysts with PdO species by an impregnation method. The reduced Pd species on different supports were prepared by two methods (H2 reduction and NaBH4 reduction). The performance of Pd supported on a series of oxides such as Co3O4,MnO2, CeO2, TiO2, Al2O3 and SiO2 were tested in the catalytic oxidation of o-xylene. We found that reduced Pd species supported on these oxides serve as an excellent catalyst for complete oxidation of o-xylene in the temperature range 90-170 oC, indicating that the reduction pretreatments are effective for improvement of catalytic activity of Pd based catalysts at low temperature. However, reduced Pd species reduced by H2 on Pd/Co3O4-H2 and Pd/MnO2-H2 showed no better activity than PdO species in the low temperature range,because the supports were partial reduced by H2 spillover. The NaBH4 reduction method is more suitable for the preparation of the metallic Pd with high activity. CeZr mixed metal oxides were prepared by coprecipitation. The reduced Pd species and PdO species were loaded on Ce-Zr mixed oxides by using NaBH4 reduction method and post-impregnation. The reduced Pd species supported on these oxides showed better activity than PdO, confirming that the metallic Pd species is the major active site for the catalytic oxidation of o-xylene. When the ratio of Ce/Zr is 9/1, this catalyst supported reduced Pd species achieved complete oxidation of o-xylene at 150 oC. This may be attributed to high Pd dispersion and more activated oxygen species. |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/34440]  |
| 专题 | 生态环境研究中心_大气污染控制中心 |
| 推荐引用方式 GB/T 7714 | 王亚飞. Pd基催化剂上催化氧化邻-二甲苯研究[D]. 北京. 中国科学院研究生院. 2014. |
入库方式： OAI收割
来源：生态环境研究中心
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