Nd-Cr/Al2O3催化剂上苯直接氧化制苯酚的动力学研究

研究了苯直接氧化制苯酚反应的动力学行为.推测了Nd-Cr/A12O3催化剂上过氧化氢氧化苯为苯酚的反应过程,建立了该反应动力学数学模型,模型很好的解释了实验结果.结果表明,在实验条件下,该羟基化反应对反应物苯、氧化剂过氧化氢和催化剂用量都是一级反应,反应的活化能为24.41 kJ/mol.     

Nd-Cr/Al_2O_3催化剂上苯直接氧化制苯酚的动力学研究

研究了苯直接氧化制苯酚反应的动力学行为。推测了Nd-Cr/Al2O3催化剂上过氧化氢氧化苯为苯酚的反应过程,建立了该反应动力学数学模型,模型很好的解释了实验结果。结果表明,在实验条件下,该羟基化反应对反应物苯、氧化剂过氧化氢和催化剂用量都是一级反应,反应的活化能为24.41 kJ/mol。     

H2O2/Se改性钒催化剂制备及催化氧化SO2性能研究

提出了一种H₂O₂/Se改性钒催化剂制备的新方法。采用XRF、XRD、SEM、MIP和TG/DSC对催化剂进行表征分析,测定了催化剂催化氧化SO₂转化率,并与国产钒催化剂CHP-75和进口VK-38对比分析。结果表明,H₂O₂/Se改性钒催化剂V@10%H₂O₂-Se/SiO₂具有清晰的表面孔道、较大的孔容、较小的活性组分晶体尺寸和较低熔融相变温度,使其具有较高的催化氧化SO₂活性。该催化剂催化活性高于国产CHP-75,与进口VK-38媲美。高效钒催化剂的设计为国产钒催化剂替代国外进口催化剂提供了一种可能。     

Fe-ZSM-5分子筛上N_2O一步氧化苯制苯酚反应失活动力学研究

根据实验现象和对积炭物组成进行的GC-MS分析结果,提出了N2O和苯在Fe-ZSM-5分子筛催化剂上进行催化氧化反应的的失活动力学模型,即产物苯酚引起的连串失活。采用固定床积分反应器系统测定了由催化剂失活引起的N2O转化率随运行时间的变化,所得实验数据用于失活动力学模型参数估值。模型表明:较低反应温度和苯相对N2O过量都可减缓催化剂的失活速率。模型统计检验表明:所得失活动力学方程在显著性水平α=0.05下有较高的拟合精度和可信度。该模型对深入了解N2O一步氧化苯制苯酚反应及指导反应器和再生器设计均具有重要的意义。     

草酸二甲酯加氢制乙二醇Cu/SiO2催化剂失活研究

采用沉淀沉积法制备了草酸二甲酯制乙二醇Cu／SiO₂催化剂。在反应温度210 ℃、压力2.0 MPa、空速0.01 mol·(g·h)^-1和氢酯物质的量比60的条件下,对催化剂的失活规律进行了研究,采用XRD、BET和TG-DTG等手段对反应前、后的催化剂进行表征,结果表明,铜烧结和高聚物可能是导致催化活性降低的主要原因。     

Pt-CeO2/TiO2催化剂催化湿式氧化苯酚废水的研究

以TiO2为载体,利用分步浸渍法制备了Pt-CeO2/TiO2、Pt-ZrO2/TiO2、Pt-La2O3/TiO2、Pt-Pr2O3/TiO2和Pt-SnO2/TiO2催化剂,并催化湿式氧化高浓度苯酚废水。Pt-CeO2/TiO2催化剂的活性最好,在反应温度为160℃、氧分压为2.25 MPa,反应时间为2 h的条件下,苯酚和COD的去除率分别为87.53%和72.06%。进一步研究助剂含量对催化剂性能的影响,当CeO2负载量为12.5%时,催化剂Pt-CeO2/TiO2的催化性能最佳。XRD和TEM结果表明,助剂CeO2的引入起到降低Pt的粒径,提高Pt在载体表面的分散度的作用。     

对失活Co-Mo-K/Al2O3硫化物催化剂的剖析研究

本文通过多种测试技术研究了工业Co-Mo-K/Al2O3耐硫变换催化剂,失活样中各元素的存在状态、含量和物相变化.发现,在原催化剂中钾、硫从内部向表面迁移并有流失,γ-Al2O3转变为(Al2O3)10R,MoS2、Co9S8变为含活性硫物种少的物相;从反应气中夹带的铁、铬、硅和镍杂质沉积在表面上.由此导致催化剂对H2O和CO的吸附与反应能力的下降,最终造成严重失活.     

对失活Co-Mo-K/Al2O3硫化物催化剂的剖析研究

本文通过多种测试技术研究了工业Co -Mo -K Al2 O3 耐硫变换催化剂 ,失活样中各元素的存在状态、含量和物相变化。发现 ,在原催化剂中钾、硫从内部向表面迁移并有流失 ,γ -Al2 O3 转变为 (Al2 O3 ) 10R ,MoS2 、Co9S8变为含活性硫物种少的物相 ;从反应气中夹带的铁、铬、硅和镍杂质沉积在表面上。由此导致催化剂对H2 O和CO的吸附与反应能力的下降 ,最终造成严重失活。     

六氟丙烯气相环氧化反应诱导期及CuO/SiO2催化剂失活机理

铜基催化剂在催化烯烃环氧化反应上具有优异的催化性能和广阔的应用前景。目前,已有专利将负载型铜基催化剂应用于六氟丙烯(HFP)气相环氧化反应,并且表现出优异的催化性能,但是反应存在诱导期及催化剂在后期活性明显降低等问题,限制了其进一步的应用发展。通过等体积浸渍法制备CuO/SiO₂催化剂,并通过FT-IR、XRD、TEM和TG等对CuO/SiO₂催化剂的物理-化学性质进行分析,系统研究其在HFP气相环氧化反应中存在诱导期及失活的原因。结果表明,Cu-F物种是反应的活性中心,而该物种由原料气(空气与HFP)和CuO反应才能产生,这是反应过程中产生诱导期的原因所在;而反应后Cu颗粒的聚集长大是催化剂活性降低的主要原因。     

微波诱导SiC改性Co-Ce/Al2O3催化剂催化氧化甲苯性能的研究

采用共沉淀法制备SiC改性5%Co-2.5%Ce/Al₂O₃催化剂,研究了不同SiC负载量改性催化剂的吸波升温性能和催化氧化甲苯性能。结果表明,随着SiC负载量的增加,催化剂吸波升温性能逐渐增强。SiC最佳负载量为5%时,催化剂催化氧化甲苯性能最佳,催化剂具有较大的比表面积和适宜的微孔结构。甲苯催化氧化活性评价结果表明,5%Co-2.5%Ce/5%SiC-Al₂O₃催化剂对不同甲苯浓度具有较强适应性,对中低浓度的甲苯降解效果显著。空速低于15 000 h^-1时催化剂能发挥高效催化作用,微波功率在120～385 W有利于甲苯的催化氧化。     

Advances in Oxidation Catalysis; Oxidation of Benzene to Phenol by Nutrous Oxide

Recent decades show impressive progress in oxidation catalysis, resulting in many novel industrial technologies. However, there is a difficult and challenging field, that of oxidation reactions which cannot be selectively implemented via traditional approaches. In the present paper, we discuss recent progress achieved in this particular field through the discovery of unique oxidation chemistry involving nitrous oxide.     

DCV-GCMD方法模拟近临界条件下乙烯、苯与乙苯在圆柱形孔道中苯烃化反应条件下的吸附和传递性质

Abstract A cylindrical pore model was used to represent approximately the pore of β-zeolite catalyst that had been used in the alkylation of benzene with ethylene and spherical Lennard-Jones molecules represented the components of the reaction system-ethylene, benzene and ethylbenzene. The dual control volume-grand canonical molecular dynamics (DCV-GCMD) method was used to simulate the adsorption and transport properties of three components under reaction in the cylindrical pore at 250℃and 270℃in the pressure range from 1 MPa to 8 MPa. The state map of the reactant mixture in the bulk phase could be divided into several different regions around its critical points. The simulated adsorption and transport properties in the pore were compared between the different near-critical regions. The thorough analysis suggested that the high pressure liquid region is the most suitable region for the alkylation reaction of benzene under the near-critical condition.     

A study on mechanism of charging/discharging at amorphous manganese oxide electrode in 0.1 M Na2SO4 solution

In the present work, the mechanism of charging/discharging at the amorphous manganese oxide electrode was investigated in 0.1 M Na₂SO₄ solution with respect to amount of hydrates and valence (oxidation) states of manganese using a.c.-impedance spectroscopy, anodic current transient technique and cyclic voltammetry. For this purpose, first the amorphous manganese oxide film was potentiostatically electrodeposited, followed by heat-treatment at 25–400 °C to prepare the electrode specimen with different amounts of hydrates and oxidation states of manganese. For as-electrodeposited electrode with the most hydrates, the anodic current transient clearly exhibited a linear relationship between the logarithm of current density and the logarithm of time, with a slope of −0.5, indicating that the charging/discharging is purely limited by Na⁺/H⁺ ion diffusion. From the analyses of the impedance spectra combined with anodic current transients measured on the hydrated electrode heat-treated at 25–150 °C, it was found that as the amount of hydrates decreases, the depth of cation diffusion in the electrode becomes shallower and the ratio of charge-transfer resistance to diffusion resistance also increases. This suggests that a transition occurs of pure diffusion control to a mixed diffusion and charge-transfer reaction control. For the dehydrated electrode heat-treated at 200–400 °C, the charging/discharging purely proceeds by the charge-transfer reaction. The reversibility of the redox reaction increases with increasing amount of hydrates and oxidation states of manganese, which provides us the higher power density. On the other hand, the pseudocapacitance decreases in value with increasing heat-treatment temperature, thus causing the lower energy density.     

Designing the activity/selectivity of surface acidic, basic and redox active sites in the supported K2O–V2O5/Al2O3 catalytic system

The supported K₂O–V₂O₅/Al₂O₃ catalytic system was designed to create surfaces that were 100% acidic, 100% basic, 100% redox, mixed redox-acidic and mixed redox-basic. The resulting nature of the surface sites was controlled by the impregnation of the specific additives (K-basic or V-redox/acidic), their order of impregnation and their surface coverage. The exact locations of the surface methoxy intermediates (AlOCH₃, KOCH₃ or VOCH₃) on the mixed oxide catalyst surfaces during methanol oxidation were determined with in situ Raman spectroscopy. The surface chemistry of the various surface sites and their surface reaction intermediates were chemically probed by CH₃OH oxidation steady-state and temperature programmed surface reaction (TPSR) spectroscopy studies. The specific reactivity order and the product selectivity of the various surface sites were found to be: VOCH₃ (HCHO) AlOCH₃ (CH₃OCH₃) KOCH₃ (primarily CO₂ and minor amounts of HCHO). Formation of dimethoxy methane, (CH₃O)₂CH₂, required the presence of dual surface redox-acidic sites surface redox sites to yield H₂CO and surface acidic sites to insert the surface methoxy into H₂CO to form dimethoxy methane, (CH₃O)₂CH₂. The addition of basic surface potassium oxide to Al₂O₃ possessing surface acid sites completely suppressed reactions from the surface acidic sites and formed a surface with only basic characteristics. The addition of redox surface vanadia to the supported K₂O/Al₂O₃ catalyst was able to completely suppress reactions from surface basic sites and formed a surface with only redox characteristics. These studies demonstrate that it is possible to determine the specific surface site requirements for each reaction pathway for methanol oxidation to products, and that this informative approach should also be applicable to other reactant molecules.     

The design of Ti-, V-, Cr-oxide single-site catalysts within zeolite frameworks and their photocatalytic reactivity for the decomposition of undesirable molecules—The role of their excited states and reaction mechanisms

Transition metal oxides (Ti, V, Mo, Cr, etc.) incorporated within the framework of zeolites were found to exhibit high and unique photocatalytic reactivity as single-site heterogeneous catalysts for various reactions such as the decomposition of NOx (NO, N₂O) into N₂ and O₂, the reduction of CO₂ with H₂O to produce CH₄ and CH₃OH, the preferential oxidation of CO in the presence of H₂ (PROX), the partial oxidation of various hydrocarbons with O₂ or NO or N₂O and the epoxidation and metathesis reaction of alkenes. In situ spectroscopic investigations of these photofunctional systems applying photoluminescence, XAFS (XANES and FT-EXAFS), ESR and FT-IR revealed that the photo-excited states of the transition metal oxides play a vital role in the photocatalytic reactions. The high photocatalytic efficiency and selectivity of these single-site catalysts for significant reactions, which could not be observed with semiconducting bulk photocatalysts, were found to depend strongly on the unique and isolated local structure of the catalysts constructed within the restricted framework structure of the zeolites.     

Organic-inorganic nanocomposite polymer electrolyte membranes for fuel cell applications

Organic-inorganic nanocomposite polymer electrolyte membrane (PEM) contains nano-sized inorganic building blocks in organic polymer by molecular level of hybridization. This architecture has opened the possibility to combine in a single solid both the attractive properties of a mechanically and thermally stable inorganic backbone and the specific chemical reactivity, dielectric, ductility, flexibility, and processability of the organic polymer. The state-of-the-art of polymer electrolyte membrane fuel cell technology is based on perfluoro sulfonic acid membranes, which have some key issues and shortcomings such as: water management, CO poisoning, hydrogen reformate and fuel crossover. Organic-inorganic nanocomposite PEM show excellent potential for solving these problems and have attracted a lot of attention during the last ten years. Disparate characteristics (e.g., solubility and thermal stability) of the two components, provide potential barriers towards convenient membrane preparation strategies, but recent research demonstrates relatively simple processes for developing highly efficient nanocomposite PEMs. Objectives for the development of organic-inorganic nanocomposite PEM reported in the literature include several modifications: (1) improving the self-humidification of the membrane; (2) reducing the electro-osmotic drag and fuel crossover; (3) improving the mechanical and thermal strengths without deteriorating proton conductivity; (4) enhancing the proton conductivity by introducing solid inorganic proton conductors; and (5) achieving slow drying PEMs with high water retention capability. Research carried out during the last decade on this topic can be divided into four categories: (i) doping inorganic proton conductors in PEMs; (ii) nanocomposites by sol-gel method; (iii) covalently bonded inorganic segments with organic polymer chains; and (iv) acid-base PEM nanocomposites. The purpose here is to summarize the state-of-the-art in the development of organic-inorganic nanocomposite PEMs for fuel cell applications.