【作者】 马书启；

【导师】 王祥生； 李钢；

【作者基本信息】 大连理工大学 ， 工业催化， 2008， 博士

【摘要】 过氧化氢（H₂O₂）是一种重要的绿色氧化剂,在造纸、纺织、化工、环保等行业有着广泛的用途。传统的H₂O₂生产工艺（蒽醌法）步骤繁多,能耗较大,并且产生大量废水,这些缺点导致H₂O₂生产成本增加,限制了其应用。因此,开发一种简洁高效的H₂O₂合成工艺具有十分重要的工业意义。利用氢气和氧气直接合成过氧化氢是最为理想的H₂O₂合成工艺。基于负载型贵金属钯或钯合金催化剂的路线已经持续研究了近百年,并有望投入工业化生产。最近的文献表明,负载型的金催化剂在催化氢气和氧气合成H₂O₂反应中同样具有较好的催化性能。文献中常用的载体有TiO₂、Al₂O₃、SiO₂、Fe₂O₃、活性炭等。钛硅分子筛TS-1作为一种新型的催化材料,在以H₂O₂为氧化剂的催化氧化反应中表现出优异的性能。其中,在丙烯环氧化、环己酮氨氧化、苯酚羟基化等反应中有着很好的工业前景。然而,H₂O₂成本较高,并且在存储、运输过程中存在危险等缺点制约了了TS-1/H₂O₂催化氧化体系的工业进程。本文以TS-1为载体,制备了Au/TS-1双功能催化剂,考察了金催化剂在直接合成过氧化氢反应中的性能,并对其进行了详细表征。在此基础上,以Au/TS-1为催化剂,把氢氧直接合成H₂O₂和氧化脱硫及1-丁烯的环氧化反应进行集成。论文主要结果如下:1.采用不同方法、不同载体制备了一系列金催化剂,用于催化H₂/O₂直接合成H₂O₂。结果表明,纳米金粒子粒径、载体的特性会影响催化剂的活性。采用不同方法制备的Au/TS-1催化剂中,Au晶粒较小的催化剂活性较高;以尿素沉积法制备的不同载体负载的金催化剂的活性顺序为Au/TiO₂＞Au/TS-1＞Au/Al₂O₃＞Au/Fe₂O₃＞Au/SiO₂。2.重点考察了Au/TS-1催化剂的制备条件及反应条件对氢氧直接合成H₂O₂的影响。结果表明,当催化剂中的Au物种以Au³⁺和Au⁺存时不能催化氢氧直接合成H₂O₂,金属态Au⁰是催化剂的活性金物种。在催化剂的制备过程中,提高沉淀剂尿素的用量,能够提高制备液的pH值,使制备的催化剂金粒子粒径减小,催化剂的活性和稳定性提高。使用甲醇作为反应介质能够增加H₂和O₂的溶解度,H₂O₂合成速率高于以水作为反应介质。在甲醇中加入适量的水,能够提高H₂O₂的合成速率,水/醇体积比为3∶2的混合溶剂作为反应介质时,H₂O₂的合成浓度最高,为11.42 mmol/L。3.以双功能催化剂Au/TS-1催化氢氧原位合成的H₂O₂进行小分子硫化物的氧化脱硫反应。结果表明,小分子的甲基硫醚最容易被氧化,而2-甲基噻吩由于空间位阻的影响,较难氧化。随着反应时间的延长,硫化物的氧化脱除率能够不断提高,反应6 h后,268 ppm的噻吩能被完全氧化脱除。提高反应温度能够促进硫化物的氧化,最佳反应温度为40℃,反应2 h噻吩的脱除率由常温时的73.0%增加到40℃时的88.3%。以Au/TS-1为催化剂,氢氧原位合成的H₂O₂氧化硫化物的反应机理与TS-1/H₂O₂反应体系相似,噻吩类硫被氧化为亚砜、砜、二氧化硫和硫酸。4.以双功能催化剂Au/TS-1催化氢氧原位合成的H₂O₂进行1-丁烯的环氧化反应。结果表明,提高反应温度能够促进1-丁烯的环氧化,但是1,2-环氧丁烷（BO）的选择性降低。随着反应时间的延长,BO的生成量持续增加,并且BO的生成速率基本保持不变。反应时间从30 min增加到180 min时,BO的生成量从0.28g/g_Au增加到1.65g/g_Au,生成速率则维持在0.54～0.60g/(g_Auh)。提高催化剂中的钛含量也能够促进BO的生成,当Si/Ti比由64降低到8时,BO的生成速率从0.45 g/(g_Auh)增加为0.87g/(g_Au h)。在常温条件下进行集成反应,BO的选择性为100%,没有副产物甲基醚或二醇生成。更多还原

【Abstract】 Hydrogen peroxide is an important green oxidizing agent.It is used in many industrial areas,such as textile industry,papermaking,chemical industry and environmental protection. The current industrial production of H₂O₂ involves a circular reaction pathway by the sequential hydrogenation and oxidation of alkyl-anthraquinone.However,this process has several obvious drawbacks,including complex operation steps,high cost and safety issue in transportation and storage.Consequently,alternative routes for H₂O₂ synthesis are highly desirable.The direct synthesis of H₂O₂ from O₂ and H₂ over a precious metal catalyst is an attractive alternative,which has been investigated for almost one century.Recently,supported gold nanoparticles proved to be a potential catalyst for direct H₂O₂ formation from H₂ and O₂. Familiar supports for gold catalyst are TiO₂,Al₂O₃,SiO₂,Fe₂O₃,active carbon,et al.Since titanium silicalite TS-1 was successfully prepared in 1983,it has exhibited the unique catalytic performance in many selective oxidation reactions involving H₂O₂ as the oxidant.Several reactions exhibit the potential for an industrial process,including propene epoxidation,ammoxidation of cyclohexanone and hydroxylation of phenol et al.However,the high cost and the problem of transportation and storage of commercial H₂O₂ have limited the industrial application of TS-1.In this paper,a bifunctional catalyst Au/TS-1 is prepared and employed in the direct synthesis of H₂O₂ from O₂ and H₂.The conditions of catalyst preparation and reaction are systematically studied.On the basis of the direct synthesis of H₂O₂ from O₂ and H₂,oxidative desulfurization and 1-butylene epoxidation are attempted over Au/TS-1 in the presence of O₂ and H₂.The following results have been obtained:1.Several supported gold catalysts are prepared by the method of deposition-precipitation with urea（DP urea） and used in the direct syntheis of H₂O₂ using deionized water as reaction medium at room temperature.TiO₂ supported gold catalyst exhibits the highest activity,followed by Au/TS-1,Au/Al₂O₃,Au/Fe₂O₃,and SiO₂. Preparation methods of the Au/TS-1 catalyst influence the catalytic activity in the direct synthesis of hydrogen peroxide.The catalyst,which contains smaller gold particles,.exhibits a higher catalystic activity.2.Effects of the preparation condition of Au/TS-1 catalysts and reaction conditions on the direct synthesis of H₂O₂ are systemically investigated.Results show that Au³⁺ and Au⁺ are mainly gold species on the Au/TS-1 catalysts dried at 40 and 100℃.These samples can not catalytze the formation of hydrogen peroxide.With increasing of calcination temperature from 200～400℃,the Au³⁺ and Au⁺ species are gradually reduced to metallic Au⁰,and the catalytic activity increases.Metallic gold species Au⁰ is proposed as the active species in the direct synthesis of hydrogen peroxide.With the amount of urea increasing during the preparation process of the Au/TS-1 catalyst,the final pH value of solvent increases,and samller gold nanoparticles are formed.The catalytical activity and the stability of the Au/TS-1 catalyst are also improved.The increase of Ti content in Au/TS-1 can result in the increase of catalytical activity.Instead of deionized water as reaction solvent,methanol is a rather suitable medium for H₂O₂ synthesis.However,a higher catalytic activity can be obtained using a water-methanol mixture as the solvent,and the optimal water/methanol volume ratio is 3:2.3.Oxidative desulfurization is investigated over bifunctional Au/TS-1 catalyst in the presence of H₂ and O₂.Results show that methyl sulfide（DMS） can be very seaily oxidized by H₂O₂ generated in situ.For the effect of steric hindrance,the oxidation rate of 2-methyl thiophene is lower than DMS and thiophene.With increasing reaction time,the removal of sulfide can be improved continuously.The temperatrue has a singnificant effect on the removal of thiophene.With increasing reaction temperature,the removal is higher than that at room temperature,and the optimum temperature is 40℃.The mechanism of oxidative desulfurization by in situ generated H₂O₂ over Au/TS-1 is similar with that in the system TS-1/H₂O₂.The sufides are oxidized to sub-sulfone,sulfone,sulfur dioxide and sulfuric acid.4.Using bifunctional Au/TS-1 as catalyst,epoxidation of 1-butylene is investigated in the presence of H₂ and O₂.The result shows that high temparature is disadvantageous to the synthesis of hydrogen peroxide,but favor the 1-butylene epoxidation.A highest formation rate of 1,2-butylene oxide（BO） is obtained at 40℃.With increasing reaction time,the amount of BO increases and the fomation rate keep at about 0.54～0.6 g/(g_Au h).Increasing the Ti content of Au/TS-1 can also improve the formation of BO.The selectivity of BO is 100% when the integration is performed at room temperature.更多还原