【作者】 陈冰冰；

【导师】 石川；

【作者基本信息】 大连理工大学 ， 物理化学， 2013， 博士

【摘要】 甲醛是一种常见的现代室内空气污染物,对环境和人类的健康造成了极大的危害。如何有效消除甲醛污染已经成为人们广泛关注的研究课题。目前应用比较广泛的脱除甲醛的技术有吸附法和催化氧化法。吸附法虽然简单易行,但是存在易受其他组分竞争吸附、吸附时间短且吸附剂再生困难等问题。催化氧化法虽然能够将甲醛完全氧化为无污染的二氧化碳和水,但是针对目前的研究来看,只有负载贵金属Pt的催化剂能在室温将甲醛完全氧化,而非贵金属则需要较高的温度。鉴于此,本论文开展了一种新的“存储-氧化”循环净化方法脱除室内空气污染物甲醛。利用催化剂的氧化功能,在一个具有“双功能”的负载银催化剂上完成整个“存储-氧化”循环,解决了空气中共存组分水与甲醛的竞争吸附问题,解决了催化剂原位再生问题。另外,通过制备不同种类载体负载的金催化剂,研究了甲醛在室温下的催化氧化。论文取得了如下研究成果：(1)建立了甲醛“存储-氧化”循环消除的新方法：利用非贵金属氧化物催化剂对甲醛的部分氧化性能,在室温下首先将甲醛部分氧化并存储在催化剂上；存储饱和后再将催化剂适当升温,催化活性提高,存储物种被完全氧化为C02和H20,催化剂得以再生。在此过程中,甲醛经历从气相到表面,反应后产物从催化剂表面脱附再进入气相的净化过程。我们研制了一种具有“存储-氧化”双功能的Ag-MnOx-CeO2催化剂。在存储阶段,这种双功能催化剂在室温下就能富集低浓度的甲醛并将其部分氧化为甲酸盐存储在催化剂上,H20的存在不仅没有与甲醛发生竞争吸附,而是促进了甲醛的部分氧化。在氧化阶段,催化剂适当升温(290℃),催化活性提高,存储的甲酸盐被完全氧化为C02和H20,催化剂得以再生。在甲醛浓度为17ppm、体积空速为30,000h-1、相对湿度为50%的模拟空气反应条件下,Ag-MnOx-CeO2催化剂上甲醛的单次吸附穿透时间超过20小时(1275min),催化剂历经五个“存储-氧化”循环依然保持高存储量和再生活性,且无二次污染产生。(2)采用沉积沉淀法分别以尿素和氢氧化钠为沉淀剂制备了Ce02负载的金催化剂。表征结果表明催化剂的活性受Au与载体之间的相互作用影响,以尿素为沉淀剂制备的Au/CeO2催化剂上金与载体之间的相互作用强,产生了更多的活泼表面活性氧物种,故其具有室温完全氧化甲醛的活性。原位漫反射红外光谱研究表明甲醛在Au/CeO2催化剂上的完全氧化需要经历两个步骤：甲醛首先被氧化为甲酸盐,然后甲酸盐被进一步完全氧化为二氧化碳和水；表面中间物种的完全氧化是Au/CeO2催化剂催化氧化甲醛的速率控制步骤。同时,利用原位漫反射红外光谱技术还系统研究了水的存在对反应中间物种的生成和消耗的影响。(3)采用共沉淀法制备了FeOx负载的Au催化剂,研究了焙烧温度和反应气氛中水对室温催化氧化甲醛活性的影响。研究表明,200℃焙烧的催化剂结晶度较差且表面含有大量羟基,Au和FeOx的相互作用较强,Au保持高度分散(平均粒径为3-4nm),并促进了载体FeOx的低温还原,故其在室温下有最佳甲醛氧化活性。原位漫反射红外光谱研究表明,反应气氛中水的存在显著提高了甲酸盐完全氧化这一速率控制步骤的反应速率,因此Au/FeOx催化剂在湿气中的催化活性高于在干气中的活性。(4)突破以可还原性载体负载贵金属为甲醛室温氧化催化剂的传统思路,首次研究了γ-Al2O3负载的Au催化剂甲醛室温氧化性能,结果表明,载体表面的羟基在反应中起重要作用：稳定Au并参与甲醛的部分氧化和完全氧化,从而使1wt%Au/γ-Al2O3催化剂在室温、有水条件下具有很好的甲醛氧化活性。更多还原

【Abstract】 Formaldehyde is one of the most common and most toxic indoor gaseous pollutants. Long-term exposure to indoor air containing HCHO may cause adverse effects on human health. Significant efforts have been made to remove low concentration of HCHO.Physical absorption and heterogeneous catalytic oxidation are regarded as the most promising HCHO removal technology. However, HCHO oxidation requires the use of elevated temperatures for most of the catalysts reported to date, though several supported noble metal catalysts have been demonstrated to be effective for HCHO oxidation at room temperature. The way of removal of indoor HCHO by adsorption is limited for a short life time and the absorbents’regeneration.In this work, a novel "storage-oxidation" cycling process was applied to remove HCHO based on a bi-functional catalyst. The bi-functions of the catalysts should include storage and partial oxidation of HCHO into the formates during the storage period at room temperature; and complete oxidation of the stored HCHO into CO2and H2O at elevated temperatures. Through the "storage-oxidation" cycling process, the catalyst could be in situ regenerated and the problem of competitive adsorption of H2O with HCHO was resolved. In addition, the different types of oxides supported Au catalysts prepared by deposition-precipitation and co-precipitation were investigated as catalysts for complete oxidation of HCHO at room temperature. The results were summarized as follows:(1) Catalytic removal of indoor HCHO was proposed to proceed in a "storage-oxidation" cycling process. At room temperature, HCHO is partially oxidized into the formate species over non-noble metals and stored on the catalyst. When the catalyst reaches saturation, it is regenerated in situ by heating, and the stored formate species are completely oxidized into CO2and H2O. Due to the highly dispersed silver clusters formed and its good redox properties, the Ag-MnOx-CeO2catalyst showed better HCHO oxidation properties in both the storage phase (HCHO partial oxidation to the formate at room temperature) and oxidation-regeneration phase (total oxidation of the formates into CO2and H2O at elevated temperatures). The presence of H2O (RH=50%,25℃) was found to enhance the HCHO storage capacity for Ag-MnOx-CeO2catalyst, while competitive adsorption of HCHO with H2O was observed over Ag/HZSM-5catalyst. The results of DRIFTS indicate that the partial oxidation of HCHO into the formate is accelerated by the presence of H2O over the Ag-MnOx-CeO2catalyst. The breakthrough time of the Ag-MnOx-CeO2catalyst was-20h (1275min) under the condition of17ppm HCHO/21%O2/H2O(RH=50%,25℃))/N2. Moreover, the "storage-oxidation" capacity of the Ag-MnOx-CeO2catalyst remained virtually unchanged for the five test cycles.(2) Two kinds of Au/CeO2, prepared by deposition-precipitation (DP) using urea (U) or NaOH (N) as precipitants were investigated as catalysts for HCHO oxidation. H2-TPR and XPS techniques were used to characterize the Au/CeO2samples. Due to the generation of increased amounts of active surface oxygen species resulting from the strong Au-Ce interaction, the Au/CeO2(DPU) catalyst showed higher activity than the Au/CeO2(DPN) catalyst, achieving100%conversion of HCHO into CO2and H2O at room temperature, even in the presence of water and at high GHSV (143,000h-1); moreover, the conversion was stable for at least60h. The reaction mechanism and the rate limiting steps for HCHO oxidation over the Au/CeO2catalysts were identified by means of in situ DRIFTS studies. The influence of oxygen and water on the formation and consumption of the formate reaction intermediates was also investigated.(3) FeOx-supported Au catalysts prepared by co-precipitation (CP) using Na2CO3as precipitant were investigated for catalytic HCHO oxidation. The applied calcination temperature was found to greatly influence both the chemical properties and microstructure of the catalysts. Characterization using XRD, H2-TPR and XPS suggested that lower calcination temperature improves the reducibility of the catalysts, and favors the presence of surface hydroxyl groups. Consequently, an Au/FeOx catalyst calcined at200℃afforded100%conversion of HCHO into CO2and H2O at room temperature and under humid air. In situ DRIFTS studies suggested that the moisture was essential for deep oxidation of the formate intermediates into CO2and H2O, this being the rate limiting step for catalytic HCHO oxidation.(4) Au supported on γ-Al2O3prepared by deposition-precipitation (DP) using urea is found to be a highly active catalyst for the total oxidation of HCHO at room temperature under humid air, without the need for a reducible oxide as support. In-situ DRIFTS studies suggested that the surface hydroxyl groups played key role in the partial oxidation of HCHO into the formate intermediates, which can be further oxidized into CO2and H2O with participation of nano-Au. This study challenges the traditional idea of supporting noble metals on reducible oxides for HCHO oxidation at room temperature.更多还原