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复合型催化剂上甲苯选择氧化及甲醛完全氧化性能的研究
Alternative TitleStudy on selective oxidation of toluene and complete oxidation of formaldehyde on composite catalysts
杨成功
Subtype硕士
Thesis Advisor麻春艳
2019-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name工学硕士
Degree Discipline环境工程
Keyword关键词: 甲苯 选择氧化 c h 活化 氧化 ,光热协同催化 催化 活性位 反应机理 Selective Oxidation Of t Oluene, c h Activation And Oxidation , p Hotothermal Catalysis, Catalytic Active Sites, Reaction Mechanism
Abstract

      针对目前甲苯液相选择氧化制备苯甲醇、苯甲醛、苯甲酸和苯甲酸苄酯存在反应效率低和污染排放高的问题,采用温和、无溶剂,氧气为氧化剂, Pt/TiO 2催化选择氧化甲苯制备苯甲醇、苯甲醛、苯甲酸和苯甲酸苄酯。分别采用静电吸附法和浸渍法合成了尺寸可控的 Pt/TiO 2 和 Pt/B TiO 2 还原型 TiO 2 催化剂,研究 Pt 的尺寸分布和化学价态,以及 TiO 2 的表面特性对甲苯 热催化和光热催化 选择氧化性能的影响,深入分析甲苯选择氧化的 活性氧物种 ,揭示甲苯 热催化和光热催化 选择氧化反应机理。
      (1) 采用静电吸附法合成了 Pt/TiO 2 和 Pt/B TiO 2 单原子、纳米簇和纳米粒子催化剂。热催化反应条件下, Pt/TiO 2 催化剂上的 C H 键氧化产物 苯甲醇、苯甲醛、苯甲酸和苯甲酸苄酯 选择性低于 50%50%,研究发现 Pt 单原子更易使得O 2 分子活化,生成氧化性较强的活性氧物种,使得甲苯发生过氧化反应,导致C H 键氧化产物选择性 的 降低。光热协同催化条件下, C H 键氧化产物选择性显著提高,接近于 100%100%,归因为光活性的 TiO 2 起到主要的催化作用,促进 O 2 活化 生成的活性氧物种有利于甲苯 C H 键活化。甲苯选择氧化生成苯甲醇,苯甲醇进一步氧化为苯甲醛、苯甲醛氧化 生成苯甲酸,苯甲醇和苯甲酸发生聚合反应生成苯甲酸苄酯 。 随反应时间进行,苯甲酸的生成量增加,苯甲醇的生成量减少,归因为甲苯不再继续发生氧化,而苯甲醇仍有部分继续氧化生成苯甲酸。
      (2) 采用浸渍法合成了 Pt/TiO 2 和 Pt/B TiO 2 纳米簇和纳米粒子催化剂。研究发现金属 载体相互作用影响甲苯选择氧化的催化性能。 后 处理温度 200 ° CPt TiO 2 相互作用较弱,光热协同催化条件下, C H 键氧化产物 选择性 仅为 41%归因为游离的 Pt 纳米粒子活化氧分子生产强氧化性的活性氧物种,促使甲苯过氧化生成 CO 2 ;当 Pt 与 TiO 2 载体之间存在较强的相互作用时,在 光热协同 催化条件下, 甲苯的 C H 键在 TiO 2 表面活化氧化,生成 C H 键氧化产物,获得苯甲醇、苯甲醛、苯甲酸和苯甲酸苄酯的选择性加和接近 于 100% 。
      (3) 系统 研究了环境 H 2 O 对 MCo 2 O 4 M = Mn Ce 和 Cu 催化剂 HCHO 和CO 室温催化 氧化性能的影响。 一定湿度条件下, MCo 2 O 4 催化剂的 HCHO 和 CO氧化性能 均优于 干燥 条件 下的催化氧化性能,但是 CuCo 2 O 4 的甲醛室温催化氧化性能是个例外,在干燥条件下, CuCo 2 O 4 不具有 HCHO 完全氧化活性, 在一定湿度条件下才具有 HCHO 完全氧化 活性。研究揭示, MCo 2 O 4 氧空位上 缔合吸附 的 H 2 O 有助于生成 HOH 活性位点 促进 HCHO 的 完全 氧化。甲酸盐物种是HCHO 氧化的中间体 但是,如果甲酸盐不能进一步 氧化 为 CO 2 ,吸附在活性位点上的甲酸盐物种将导致催化剂失活。在一定湿度条件下,氢键 H 2 O 和自由 OH覆盖 在 MCo 2 O 4 催化 活性 位点上, 加速了 HCHO 氧化催化剂失活。 HOH 不是 CO氧化的催化活性 位,因此,一定湿度 条件下氧空位上 吸附 H 2 O 则 阻止了 CO 完全氧化 活性氧物 种 的 生成 ,导致 CO 氧化催化剂的失活。 通过对环境 H 2 O 在HCHO 和 CO 室温催化 氧化中的关键作用 研究 ,有助于 开发 干燥或 湿度 条件 下具有 高活性和 高稳定性的 HCHO 和 CO 完全氧化 催化剂。
      Pt/TiO2 催化剂实现 了 无溶剂,氧气为氧化剂,甲苯选择氧化制备苯甲醇、苯甲醛、苯甲酸和苯甲酸苄酯高附加值产品,符合清洁生产的要求,研究提出了Pt/TiO 2 催化剂上甲苯选择氧化的热催化和光热催化的 活性氧种 以及反应机理,为甲苯绿色选择氧化反应过程 的研究 提供了材料基础和理论支撑。

Other Abstract

      At present, the selective oxidation of toluene to benzyl alcohol, benzaldehyde, benz oic acid and benzyl benzoate is an environmental unfriendly process . The problems of thermal oxidation of toluene are low toluene conversion and high pollution emission. Therefore, solvent free selective oxidation of toluene to benzyl alcohol, benzaldehyde, benzoic acid and benzyl benzoate over Pt/TiO 2 catalysts using O 2 under mild condition is significant . Pt/TiO 2 and Pt/B TiO 2 (reduced TiO 2 catalysis with different Pt dispersion were synthesized by electrostatic adsorption and impregnation methods. The size distribution , the chemical valence of Pt and the surf ace properties of TiO 2 were characterized. The effects of material properties on the thermal and photothermal selective oxidation of toluene were studied. The catalytic active sites of Pt/TiO 2 and the reaction mechanism for thermal and photothermal selecti ve oxidation of toluene under different reaction conditions were proposed
      (1)We synthesize single Pt atom s (SA) SA), subnanometric Pt clusters (NC) and Pt nanoparticle s (NP) supported on TiO 2 or reduced TiO 2 catalysts by electrostatic adsorption method . The products of C H oxidation of toluene are benzyl alcohol,benzaldehyde, benzoic acid and benzyl benzoate . T he selectivity to thermal oxidation of primary C H bond of toluene over Pt/TiO 2 catalysts is less than 50%. It is found that O 2 molecule activated on the single Pt atom catalysts are more likely to oxidize toluene to generate CO 2 and hydrocarbon, which leads to a decrease in the selectivity of the C H bond oxidation products. T he selectivity of photothermal oxidation of C H bond products is close to 100 which is attributed to O 2 activation occured on TiO 2 The active oxygen species generated on TiO 2 facilitate the C H bond oxidation of toluene. First, t he selective oxidation of toluene to produce benzyl alcohol , then benzyl alcohol is further oxidized to benz aldehyde next benzaldehyde is oxidized to benzoic acid B enzyl alcohol and benzoic acid are polymerized to form benzyl benzoate.Because the selective oxidations of toluene do not go on after a period of time, the yield of benzyl alcohol decreases with the reaction time increases. Because benzyl alcohol can be oxidized to benzoic acid after the selective oxidation of toluene stopping, t he yield of benzoic acid increases with the reaction time increases .
      (2)Subnanometric Pt clusters (NC) and Pt nanoparticle s (NP) supported on TiO2 or reduced TiO 2 catalysts were synthesized by impregnation method. The metal support interaction was found to affect the catalytic performance of selective oxidation of toluene. For the Pt/TiO 2 catalysts calcinated at 2 00 º C , the interaction between Pt and TiO 2 is weak. O xygen molecules activated on free Pt nanoparticles can oxidiz e toluene to form CO 2 and hydrocarbon . T hus, t he selectivity to photothermal oxidation of C H bond of toluene is only 41% 41%. When there exist a strong interaction between Pt and TiO 2 , the C H bonds of toluene is activated and oxidized on the surface of TiO 2 to form C H bond oxidation products (benzyl alcohol, benzaldehyde, benzoic acid and benzyl benzoate). The selectivity of C H bond oxidation products is close to 100%.
      (3)The abatement of HCHO and CO at room temperature by catalytic oxidation over metal oxides can be achieved. However, the catalytic performance of metal oxides is influenced by H 2 O vapor in the reaction air and the mechanism o f H 2 O role is still debated. In this paper, the effect of H 2 O on the catalytic performance of a MCo 2 O 4 (M = Mn, Ce and Cu) catalyst for HCHO and CO oxidation at room temperature was investigated. For both HCHO oxidation and CO oxidation, all the MCo 2 O 4 cat alysts in humid air are less active than in dry air except for HCHO oxidation catalyzed by CuCo 2 O 4 catalyst. The CuCo 2 O 4 is inactive for HCHO oxidation in dry air, but active for HCHO oxidation in humid air. The associatively adsorbed H 2 O on MCo 2 O 4 contrib uted to the active HOH sites for HCHO oxidation.Formate species are intermediates of HCHO oxidation. However, if formate cannot be further transferred into CO 2 , the formate adsorbed on active sites will result in catalyst deactivation. In humid air, hydro gen bonded OH and free OH generated and covered active sites accelerated the catalyst deactivation in HCHO oxidation. The CO was oxidized by the active oxygen species but not included OH species. Thus, the H 2 O adsorbed on oxygen vacancies blocked the generation of active oxygen species, which resulted in MCo 2 O 4 deactivation for CO oxidation in humid air. This work provide a fundamental understanding of the key role of H 2 O in the HCHO and CO oxidation at room temperature, which is helpful for the design of high activity and long lifetime catalyst used in dry or humid conditions. 
    Solvent free oxidation of toluene to pr oduce benzyl alcohol, benzaldehyde,benzoic acid and benzyl benzoate over Pt/TiO 2 catalysts with oxygen meets the requirements of clean er p roduction. Th is research proposed the thermal and photothermal catalytic active sites and reaction mechanism of selective oxidation of toluene over Pt/TiO 2 catalysts, which is helpful for pereparation of material with good catalytic performance in the gree n selective oxidation of toluene.
 

Pages105
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/42330
Collection环境纳米技术与健康效应重点实验室
Recommended Citation
GB/T 7714
杨成功. 复合型催化剂上甲苯选择氧化及甲醛完全氧化性能的研究[D]. 北京. 中国科学院生态环境研究中心,2019.
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