【作者】 苏元成；

【导师】 殷永泉；

【作者基本信息】 山东大学 ， 环境科学， 2007， 硕士

【摘要】 近年来，我国经济的高速发展造成了大气污染，许多城市受到光化学烟雾污染的威胁，装修材料的使用又污染了室内环境。VOCs（Volatile organiccompounds）是光化学烟雾的前体物质，又是室内环境的主要污染物。苯、甲苯和二甲苯属于室内空气中浓度较高的VOCs，因此，苯、甲苯和二甲苯光降解及光催化降解的研究对大气污染防治具有十分重要的指导意义。研究了苯、甲苯和二甲苯在直接光降解时反应物初始浓度和反应体系的影响；研究了苯、甲苯和邻二甲苯光降解中间产物浓度变化与光降解机理；研究了在无催化剂、纯锐钛矿催化剂、纯金红石以及复合催化剂时苯、甲苯和二甲苯的光催化降解情况；考察了反应物初始浓度、以及不同催化剂组成时苯、甲苯和二甲苯的光催化降解情况；研究了苯、甲苯和邻二甲苯光催化降解机理。本论文的主要研究结果如下：（1）在苯、甲苯和二甲苯光降解或光催化降解时，由于光照可使反应器升温，而温度的变化又会影响反应物在反应器壁或催化剂表面的吸附平衡，故需控制反应器内温度。吸附平衡实验确定苯达到吸附平衡的时间为30min，甲苯40min，邻二甲苯50min，间二甲苯和对二甲苯均为45min。（2）苯和甲苯直接光降解时，初始浓度越大，光降解越快。在相同的条件下苯系物的降解速率的顺序为邻二甲苯＞间二甲苯＞对二甲苯＞甲苯＞苯，主要原因是甲基供电基团的引入降低了苯环π-π共轭体系的键能，破坏了苯环的空间结构，从而使整个体系变得不对称。（3）苯、甲苯和二甲苯在空气体系与通氮气20min后的氮气体系中的降解速率相差不大，而在120℃通氮气20min后的氮气体系中的降解速率明显变小。主要原因是H₂O作为OH·基的发生源，对光降解有促进作用，120℃通氮气可使吸附在反应器壁的水分子数量明显减少，故光降解速率降低。（4）苯光降解主要产物是丙炔、丁二烯、2-甲基己烷、3-甲基己烷和庚烷；甲苯光降解主要产物是丙炔、苯和苯甲醛；邻二甲苯光降解主要产物为丙炔、3-甲基丁醛、间二甲苯、2-甲基乙苯、甲苯和苯。苯、甲苯和邻二甲苯光降解主要产物都有丙炔，是反应物吸收光子后分解形成的。（5）苯系物在无催化剂、锐钛矿催化剂和金红石催化剂三种条件下的降解速率大小关系为锐钛矿＞金红石＞无催化剂，这主要是由于金红石电子与空穴比较容易复合。（6）在锐钛矿催化剂中掺入一定量的金红石可提高催化剂的光催化活性，锐钛矿含量80％、金红石含量20％的复合催化剂对苯和对二甲苯的光催化活性最高，而锐钛矿含量90％、金红石含量10％的复合催化剂对甲苯、邻二甲苯和间二甲苯的光催化活性最高。（7）使用GC—MS分析苯、甲苯和邻二甲苯光催化降解气相中产物以及吸附在催化剂表面的产物。研究发现，气相中苯降解的主要产物为丙炔，甲苯降解的主要产物为丙炔和苯，邻二甲苯气相中降解的主要产物为丙炔、2-甲基乙苯、间二甲苯、甲苯和苯。吸附在催化剂表面上的产物比气相中产物多，苯的主要产物为3-甲基己烷、2，3-二甲基己烷、1-甲基-2-丙基环戊烷、2，4-二甲基己烷、2，5-二甲基己烷、3-甲基庚烷和2，4-二甲基庚烷；甲苯主要产物为苯、2，3，4-三甲基己烷、乙苯和对二甲苯；邻二甲苯主要产物为间二甲苯、2-甲基乙苯、2-甲基苯甲醛、甲苯和苯。从吸附在催化剂表面的苯和甲苯光催化降解产物中检测出了饱和的烷烃，说明苯和甲苯光催化降解的同时存在着加氢反应。邻二甲苯在气相和吸附在催化剂表面产物中都发现了苯、甲苯和间二甲苯，说明邻二甲苯既可发生脱甲基反应，也可发生异构反应。更多还原

【Abstract】 In recent years, the rapid economic development in China has brought atmospheric pollution incidents. Many cities are facing the threat of photochemical smog, and the indoor environment is being polluted by usage of new decoration materials. Volatile organic compounds （VOCs） are precursors of photochemical smog and main pollutants of indoor air. Benzene, toluene and xylene are the main and important VOCs in indoor air. Hence, study of photo-degradation and photo-catalytic degradation of benzene, toluene and xylene is of great significance in atmospheric pollution control.In this study, influence of initial concentration and reaction system were studied during photo-degradation of benzene, toluene and xylene. Intermediate products and photo-degradation mechanism of benzene, toluene and o-xylene were studied. Photo-catalytic degradation of gas-phase benzene, toluene and xylene were studied in the conditions of no catalyst, pure anatase catalyst, pure rutile catalyst and multi-composite catalyst. The influence of initial concentration of reactants and catalyst composite on efficiency of photo-degradation was investigated in photo-catalytic degradation of gas-phase benzene, toluene and xylene. Reaction mechanism of photo-catalytic degradation of bezene, toluene and o-xylene was also studied.The key findings in this study were summarized as follows:（1） During photo-degradation and photo-catalytic degradation of benzene, toluene and xylene, the temperature of the reactor should be controlled at a value because the increase of the temperature caused by illumination would influence the adsorption equilibrium. Through experiments of adsorption equilibrium, the time needed to reach adsorption equilibrium for benzene, toluene, o-xylene, m-xylene and p-xylene was found to be 30min, 40min, 50 min, 45min and 45min, respectively.（2） During photo-degradation of benzene and toluene, the increase of initial concentration would cause the increase of reaction rates. In the same reaction condition, the relation of reaction rates for benzene series（benzene, toluene and xylene） was: m-xylene > o-xylene > p-xylene > toluene > benzene, because the introduction of methyl lowered the energy of benzene π-π- conjugated system and destroyed spatial structure of the benzene ring.（3） The photo-degradation of benzene, toluene and xylene in air were similar to nitrogen system （N₂ flow for 20min）. If the temperature of the system was controlled at 120℃ under N₂ flow, the photo-degradation rates decreased, because H₂O was source of OH·, H₂O was driven off at high temperature in the reactor, and the reaction rates slowed down.（4） The main intermediate products of photo-degradation of benzene were 1-propyne, 1,3-butadiene, 2-methyl-hexane, 3-methyl-hexane and heptan. The main intermediate products of photo-degradation of toluene were 1 -propyne, benzene and benzaldehyde. The main intermediate products of o-xylene were 1-propyne, 3-methyl-butanal, m-xylene, 2-methyl-ethylbenzene, toluene and benzene. 1-propyne was the main intermediate product during photo-degradation of benzene, toluene and o-xylene and it resulted from photo-decomposition of the reactants.（5） The relation of degradation rates of benzene series in case of no catalyst, anatase and rutile was anatase > rutile > no catalyst, because the electron and hole was easy to combine to rutile.（6） A certain amount of rutile doped in anatase catalyst could improve the photo-catalytic activity. The catalyst with 80% anatase and 20% rutile showed the best photo-catalytic activity to benzene and p-xylene, and the catalyst with 90% anatase and 10% rutile gave the best photo-catalytic activity to toluene, m-xylene and o-xylene.（7） GC—MS were used to analyze the intermediate products of photo-catalytic degradation of benzene, toluene and o-xylene. In gas phase, the main product of benzene was 1-propyne, the main products of toluene were 1-propyne and benzene, the main products of o-xylene were 1-propyne, 2-methyl-ethylbenzene, m-xylene, toluene and benzene. There were more intermediate species on catalyst surface than in gas phase. The main products of photo-catalytic degradation of benzene were 3-methyl-hexane, 2,3-dimethyl-hexane, 1-methyl-2-propyl-cyclopentane, 2,4-dimethyl-hexane, 2,5-dimethyl-hexane, 3-methyl-heptane and 2,4-dimethyl-heptane. The main products of toluene were benzene, 2,3,4-trimethyl-hexane, ethylbenzene and p-xylene. The main products of o-xylene were m-xylene, 2-methyl-ethylbenzene, 2-methyl-benzaldehyde, toluene and benzene. During photo-catalytic degradation of benzene and toluene, alkane was detected in the adsorption species on catalyst surface, which indicated that hydrogen addition reaction existed during photo-catalytic degradation of benzene and toluene. Benzene, toluene and m-xylene were detected both in gas phase intermediate products and asorption species on catalyst surface during photo-catalytic degradation of o-xylene, which indicated demethylation and structure changing reaction existed during photo-catalytic degradation of o-xylene.更多还原