连续放电和吸附存储—放电催化降解甲苯的机理研究

发布时间：2018-07-21 20:42

【摘要】：挥发性有机物(Volatile Organic Compounds,VOCs)是O3和PM2.5等二次污染的重要前体物,随着我国经济发展,VOCs排放量逐年上升,导致的大气污染问题逐渐凸显,VOCs治理迫在眉睫。等离子体催化技术作为新的空气污染净化技术之一,可在常温常压下转化VOC,具有转化效率高、占地面积小、反应快速、降低二次污染等显著优点,其相关研究受到国内外学者的广泛关注。但由于等离子体催化体系复杂,缺乏直接的实验证据,VOCs在等离子体中的降解途径以及催化剂在等离子体降解中的作用等机理研究尚未清楚,影响该技术的推广和应用。本文采用低温等离子体协同γ-Al2O3及其负载Ag、NiO、MnOx活性组分后的催化剂降解甲苯,综合评价催化剂在连续放电降解法和吸附存储-放电法中催化降解甲苯的性能,考察不同降解方法之间催化降解甲苯过程的区别,分析催化剂的吸附性及不同活性组分的添加对反应过程的影响,并通过自行设计的原位红外反应池,对连续放电及吸附存储-放电催化降解甲苯过程中催化剂表面的吸附物种连续在线分析,并结合GCMS分析结果,对催化剂表面中间物种物种的变化进行研究,探讨甲苯的降解途径及降解过程中的关键物种及控制步骤。采用浸渍法制备Ag/γ-Al2O3、NiO/γ-Al2O3、MnOx/γ-Al2O3催化剂,甲苯的降解效率从大到小依次为MnOx/γ-Al2O3NiO/γ-Al2O3Ag/γ-Al2O3γ-Al2O3空管,甲苯在等离子体催化作用下的降解效果与催化剂对甲苯的吸附和O3的分解能力有关。吸附存储-放电法在甲苯去除率、碳平衡和二氧化碳选择性方面优于连续放电法,特别是甲苯去除率可达100%。吸附存储在催化剂表面的甲苯能有效利用等离子体产生的活性物种,间歇放电能够使催化剂表面的活性位点暴露,减少中间产物或副产物的沉积,从而促进甲苯的氧化分解。活性组分的添加促进了甲苯的降解。Ag可以与甲苯分子形成π配位络合,增加催化剂的吸附容量和吸附强度,NiO改变催化剂表面的亲电性和氢吸附作用,弱化苯环结构的稳定性;MnOx的加入提升了催化剂的氧化还原能力和降解臭氧的能力,促使中间产物迅速氧化降解。等离子体催化降解甲苯的主要产物为苯甲醇、苯甲醛、苯甲酸、酯类及胺类等。结合GC-MS和原位红外分析结果,等离子体催化氧化甲苯时,放电降解模式影响其降解途径。连续放电中间产物种类多,吸附存储-放电模式的中间产物较少,相比连续放电法降解甲苯更为彻底,且未检测到胺类物质的生成。等离子体降解甲苯的路径主要路径为甲苯→苯甲醇→苯甲醛→苯甲酸→小分子醇、酸、酯→CO2和H2O。
[Abstract]:Volatile organic compounds (VOCs) are important precursors of secondary pollution, such as O3 and PM2.5. With the economic development of China, VOCs emissions are increasing year by year. As one of the new air pollution purification technologies, plasma catalytic technology can convert VOC at room temperature and atmospheric pressure. It has many advantages, such as high conversion efficiency, small area, rapid reaction, reducing secondary pollution, and so on. The related research has been widely concerned by scholars at home and abroad. However, due to the complexity of plasma catalytic system, the mechanism of VOCs degradation in plasma and the role of catalyst in plasma degradation are not clear, which will affect the popularization and application of this technology. In this paper, the catalytic degradation of toluene by low temperature plasma in combination with 纬 -Al 2O 3 and the active components of Agn NiO- MNO x was evaluated. The catalytic degradation of toluene by continuous discharge degradation and adsorption storage discharge was evaluated. The differences of catalytic degradation of toluene among different degradation methods were investigated. The adsorption of catalyst and the effect of addition of different active components on the reaction process were analyzed, and the in-situ infrared reaction cell was designed. In the process of continuous discharge and adsorptive storage-discharge catalytic degradation of toluene, the adsorption species on the catalyst surface were continuously analyzed on line, and the changes of intermediate species on the catalyst surface were studied based on the results of GCMS analysis. The degradation pathway, key species and control steps of toluene degradation were discussed. Ag/ 纬 -Al _ 2O _ 3NiO / 纬 -Al _ 2O _ 3 Mn-Ox/ 纬 -Al _ 2O _ 3 catalysts were prepared by impregnation method. The degradation efficiency of toluene was in the order of MnOx/ 纬 -Al _ 2O _ 3NiO / 纬 -Al _ 2O _ 3Ag / 纬 -Al _ 2O _ 3 纬 -Al _ 2O _ 3 hollow tubes. The degradation effect of toluene under plasma catalysis was related to the adsorption of toluene and the decomposition of O _ 3. Adsorption storage-discharge method is superior to continuous discharge method in toluene removal rate, carbon balance and carbon dioxide selectivity, especially in toluene removal rate up to 100. Adsorption of toluene stored on the surface of the catalyst can effectively utilize the active species produced by plasma. Intermittent discharge can expose the active sites on the surface of the catalyst and reduce the deposition of intermediate or by-products, thus promoting the oxidative decomposition of toluene. The addition of active component can promote the degradation of toluene. Ag can form 蟺 coordination complexation with toluene molecule, increase the adsorption capacity and adsorption strength of the catalyst and change the electrophilicity and hydrogen adsorption of the catalyst surface. The weakening of the stability of benzene ring structure and the addition of MnOx enhanced the redox ability of the catalyst and the ability of ozone degradation, and promoted the intermediate product to be oxidized and degraded rapidly. The main products of plasma catalytic degradation of toluene are benzyl alcohol, benzaldehyde, benzoic acid, esters and amines. Combined with the results of GC-MS and in situ infrared analysis, the mode of discharge degradation affected the degradation pathway of toluene catalyzed by plasma. There are many kinds of intermediate products in continuous discharge and less intermediate products in adsorptive storage-discharge mode. The degradation of toluene by continuous discharge is more thorough than that by continuous discharge and the generation of amines is not detected. The main pathway of plasma degradation of toluene is toluene, benzyl, benzaldehyde, benzoic acid, carboxylic acid, ester CO _ 2 and H _ 2O.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X701

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