铁改性分子筛直接催化分解一氧化二氮

采用以离子交换法制备的Fe-ZSM-5、Fe-MCM-22和Fe-Beta分子筛催化剂,系统地考察了分子筛构型、酸性和酸中心分布对N2O直接催化分解的影响.采用N2吸附、红外光谱仪(FT-IR)、NH3程序升温脱附实验(NH3-TPD)、H2程序升温还原实验(H2-TPR)和原位漫反射红外光谱(in situ DRIFTS)等方法考察了铁离子负载量、Si与Al摩尔比和分子筛构型对N2O催化分解的影响.结果表明,价键补偿Fe3 离子是N2O分解的主要活性组分;分子筛活性随Si和Al摩尔比的减少和铁离子负载量的增加而增加;Fe-Beta分子筛的催化活性明显高于Fe-ZSM-5和Fe-MCM-22分子筛;分子筛酸性和酸中心分布影响铁离子的分布,从而导致不同构型分子筛催化分解N2O的活性具有明显差异.     

Metal Exchanged ZSM-5 Zeolite Based Catalysts for Direct Decomposition of N2O

Co+Pt/ZSM-5 and Ag+Pt/ZSM-5 type catalysts were prepared by ion exchange method followed by calcination. These Co and Ag based catalysts, promoted by a small amount of Pt have been studied for their catalytic activity towards N₂O decomposition. Both the catalysts show high catalytic activity, however, cobalt–platinum based catalyst shows relatively better activity at higher temperature. At 550 °C almost 100% conversion of N₂O is achieved over Co+Pt/ZSM-5 with a maximum of 0.08479 mmole of N₂O decomposed per gram of the catalyst per unit time. These catalytic materials have been characterized for their structure, composition, morphology and other details, using XRD, SEM, EDX, ICP, BET techniques. Much improved catalytic activity for the bimetallic zeolite than the mono-metal containing compositions clearly demonstrate the synergistic effect of these transition metals, while high surface area of ZSM-5 is also responsible for the improved N₂O decomposition activity.     

NO-Assisted N2O Decomposition over ex-Framework FeZSM-5: Mechanistic Aspects

The decomposition of N₂O over an ex-framework FeZSM-5 catalyst is strongly promoted by NO. Activity data show that the promoting effect of NO is catalytic, and that besides NO₂, O₂ is formed much more extensively in the presence, than in the absence of NO. Transient in situ FT-IR/MS measurements indicate that NO is strongly adsorbed on the catalyst surface up to at least 650 K, showing absorption frequencies at 1884 and 1876 cm^–1. A change in gas phase composition from NO to N₂O results in the formation of adsorbed NO₂, identified by a sharp IR band at 1635 cm^–1. Switching back to the original NO gas phase induces a rapid desorption of NO₂, restoring the original NO absorption frequencies. During the IR measurements, bands typical of nitro- or nitrate groups were not observed. Multi-Track (a TAP-like technique) experiments show that the presence of NO or NO₂ on the catalyst surface significantly enhances the rate of oxygen desorption at the time of N₂O exposure to the catalyst. The spectral changes and transient experiments are discussed and catalytic cycles are proposed, to explain the formation of NO₂ and the (enhanced) formation of oxygen. The latter can be either explained by an indirect effect (electronic, steric) of NO adsorbed on sites neighboring the active sites, or by a direct effect involving reaction of adsorbed NO₂ groups with neighboring oxidized sites yielding O₂.     

Decomposition of H2O2 by Iron Centered Catalysts

The kinetics and mechanism of the catalytic decomposition of H₂O₂ by Fe³⁺ ion, haemin and catalase are discussed. A general mechanism is set up. The kinetic features of the three catalytic systems are discussed in terms of this mechanism.     

Low-Temperature Catalytic Decomposition of N2O

Theoretical Foundations of Chemical Engineering - A series of oxide catalysts modified with potassium cations, 1–5% K2О/CoFe2O4, with a spinel structure were obtained via...     

Oxidative Decomposition of N,N'-Dimethylformamide over Pt Catalysts with H2 Addition to the Feed

Catalysis of decomposition of dilute N, N'-dimethylformamide was explored. Among the catalysts investigated, Pt displayed the highest activity at low temperatures (~200 °C) and DMF conversion was promoted by H₂ addition to the feed. As the Pt support material, H-ZSM-5 exhibited the best performance at around 200 °C in terms of harmless decomposition.     

Catalytic Conversion of N2O to N2 over Metal-Based Catalysts in the Presence of Hydrocarbons and Oxygen

The catalytic conversion of N₂O to N₂ in the presence or the absence of propene and oxygen was studied. The catalysts examined in this work were synthesized impregnating metals (Rh, Ru, Pd, Co, Cu, Fe, In) on different supports (Al₂O₃, SiO₂, TiO₂, ZrO₂ and calcined hydrotalcite MgAl₂(OH)₈·H₂O). The experimental results varied both with the type of the active site and with the type of the support. Rh and Ru impregnated on -alumina exhibited the highest activity. The performance of the above most promising catalysts was studied using various hydrocarbons (CH₄, C₃H₆, C₃H₈) as reducing agents. These experimental results showed that the type of reducing agent does not affect the reaction yield. The temperature where complete conversion of N₂O to N₂ was measured was independent of the reductant type. The activity of the most active catalysts was also measured in the presence of SO₂ and H₂O in the feed. A shift of the N₂O conversion versus temperature curve to higher temperatures was observed when SO₂ and H₂O were added, separately or simultaneously, to the feed. The inhibition caused by SO₂ was attributed to the formation of sulfates and that caused by water to the competitive chemisorption of H₂O and N₂O on the same active sites.     

Sn改性Raney Ni催化分解N,N-二甲基甲酰胺的研究

为了研究Sn含量和还原温度对Sn-RaneyNi催化剂的物理化学结构和催化分解N,N-二甲基甲酰胺(DMF)活性的影响,利用沉淀法制备了一系列不同Sn含量的Sn-RaneyNi催化剂,采用N2物理吸附、X射线衍射(XRD)和氢气程序升温还原(H2-TPR)等方法对不同Sn含量和不同还原温度制得的Sn-RaneyNi催化剂的比表面积、物相组成和还原性能进行了表征。以N,N-二甲基甲酰胺(DMF)为模型化合物,对Sn-RaneyNi催化剂的催化分解活性进行了评价。XRD表征结果表明,n(Sn)/n(Ni)为0.1的催化剂分别在723K和823K下还原生成Ni3Sn4和Ni3Sn合金晶相;n(Sn)/n(Ni)为0.15的催化剂在723K下还原形成Ni3Sn2合金晶相。H2-TPR结果表明,Ni-Sn合金的形成削弱了Sn和Ni与氧的结合能,使得Sn和Ni的还原峰向低温移动。催化分解DMF实验结果表明,当n(Sn)/n(Ni)为0.1、还原温度为723K时,Sn修饰RaneyNi催化剂能够将高浓度DMF(5%(wt))完全分解(分解率达100%),氢气的选择性达到86.8%。     

Transient Studies of Direct N2O Decomposition over Pt–Rh Gauze Catalyst. Mechanistic and Kinetic Aspects of Oxygen Formation

For elucidating the mechanistic aspects of oxygen formation during N₂O decomposition over commercial woven Pt–Rh gauze, transient experiments were carried out in the temporal analysis of products (TAP) reactor by pulsing N₂ ¹⁶O over ¹⁸O-pretreated gauze catalyst at temperatures typical of industrial ammonia burners (1073–1273 K). The transient responses of N₂O and the products of its decomposition (O₂ and N₂) were fitted to two different mechanistic models. From the isotopic studies and the fitting of transient experiments, two separate routes of oxygen formation during catalytic N₂O decomposition have been identified. Oxygen is produced via both (i) interaction of N₂O with adsorbed oxygen species formed from N₂O and (ii) recombination of adsorbed oxygen species on the catalyst surface. The relative contribution of these reaction pathways depends on the reaction temperature.     

N2O Decomposition over Fe-Ferrierite: Primary and Secondary Reactions with Reducing Agents

The decomposition of N₂O either alone or with several reducing agents (CH₄, CO, NO and D₂) was followed by temperature-programmed desorption of surface species formed during the reactions. TPD products formed in these “primary” reactions were compared with the TPD products after “secondary” reactions of the same set of reducing agents with the surface species formed during the primary reactions. Changes in TPD products after reactions measured under various conditions were analyzed in detail. These experiments provided a background for studies of the nature and reactivity of surface species formed during N₂O reactions over Fe-ferrierite. The relevance of these experimental results to the mechanism of the N₂O elimination is discussed.     

Brief Review of N_2O Decomposition Catalysts for Engines

A brief review of nitrous oxide decomposition catalysts was presented.The features of catalyst operating conditions in low-thrust engines of space vehicles and requirements to monopropellant(hydrogen peroxide,hydrazine,nitrous oxide)decomposition catalysts were considered.A scientific basis for development of a nitrous oxide decomposition catalyst and general principles for selection of efficient catalysts were formulated.The results of selecting catalyst systems for the development of decomposition catalysts for N2O as a monopropellant were presented.Preliminary selection of catalyst systems for the development of a catalyst designed for low-thrust rocket engines(LTREs)was carried out:supporter—Al2O3 and ZrO2;active substances—Co,Ni,Fe,Pd,Rh,Pt,Ru,Ir,NiO,Fe2O3,RuO2,Rh2O3,PdO,IrO2,PtO2,CoO,Al2O3,La2NiO4,Nd2NiO4,Pr 2NiO4,La2O3,TiO2,NiO,La2O3,TiO2,ZnO.With 71 references.     

超临界浸渍法制备CuO/Al_2O_3催化剂

应用超临界浸渍法制备CuO/γ-Al2O3催化剂。以Cu(NO3)2为前驱体,甲醇为助溶剂在载体Al2O3上于超临界二氧化碳中进行浸渍,研究了不同浸渍条件:超临界温度、压力、浸渍时间、前驱体和载体量之比,助溶剂量等因素对浸渍效果的影响。并以SEM和XRD分别对超临界与普通浸渍法制备的样品进行了表征。结果说明,超临界浸渍时吸附速度明显较快,吸附量大,浸渍物分布均匀且和载体作用较强。以亚甲基蓝的催化氧化降解为模型反应测定两种制法催化剂的活性,超临界条件制备的催化剂活性明显较好。所得结果表明,使用无机金属前驱体加助溶剂的方法可以代替有机金属前躯体在超临界浸渍中的使用。     

Decomposition of N2O on Perovskite-Related Oxides

Mixed metal oxides crystalizing in a perovskite-related structure have long been of interest to solid state chemists and physicists because of their technologically important physical properties. The ready availability of a family of isomorphic solids with controllable physical properties makes these oxides suitable for basic research in catalysis. These mixed metal oxides are more advantageous and are better catalytic materials than simple oxides because: (i) the crystal structure can accomodate various metal ions and can stabilize unusual and mixed valence states of active metal ion; (ii) appropriate formulation of these oxides leads to easy tailoring of many desirable properties such as valence state of transition metal ion, distance between active sites, binding energy, diffusion of oxygen in the lattice, magnetic and conducting properties of the solid; (iii) the catalytic activity can be correlated to solid state properties since many of their solid state properties are thoroughly understood; (iv) the surface of these oxides can be regenerated by suitable activation procedure.     

Decomposition of N2O on Perovskite-Related Oxides

Mixed metal oxides crystalizing in a perovskite-related structure have long been of interest to solid state chemists and physicists because of their technologically important physical properties. The ready availability of a family of isomorphic solids with controllable physical properties makes these oxides suitable for basic research in catalysis. These mixed metal oxides are more advantageous and are better catalytic materials than simple oxides because: (i) the crystal structure can accomodate various metal ions and can stabilize unusual and mixed valence states of active metal ion; (ii) appropriate formulation of these oxides leads to easy tailoring of many desirable properties such as valence state of transition metal ion, distance between active sites, binding energy, diffusion of oxygen in the lattice, magnetic and conducting properties of the solid; (iii) the catalytic activity can be correlated to solid state properties since many of their solid state properties are thoroughly understood; (iv) the surface of these oxides can be regenerated by suitable activation procedure.     

Direct N2O decomposition over ex-framework FeMFI catalysts. Role of extra-framework species

Extra-framework iron species in FeMFI prepared via an ex-framework route are essential for the formation of reactive oxygen species in direct catalytic decomposition of N₂O, while Lewis or Brønsted acid sites play a minor role in this reaction.     

Direct Oxidation of H2 to H2O2 and Decomposition of H2O2 Over Oxidized and Reduced Pd-Containing Zeolite Catalysts in Acidic Medium

Both the conversion and H₂O₂ selectivity (or yield) in direct oxidation of H₂-to-H₂O₂ (using 1.7 mol% H₂ in O₂ as a feed) and also the H₂O₂ decomposition over zeolite (viz. H-ZSM-5, H-GaAlMFI and H- ) supported palladium catalysts (at 22 °C and atmospheric pressure) are strongly influenced by the zeolite support and its fluorination, the reaction medium (viz. pure water, 0.016 M or 1.0 M NaCl solution or 0.016 M H₂SO₄, HCl, HNO₃, H₃PO₄ and HClO₄), and also by the form of palladium (Pd⁰ or PdO). The oxidized (PdO-containing) catalysts are active for the H₂-to-H₂O₂ conversion and show very poor activity for the H₂O₂ decomposition. However, the reduced (Pd⁰-containing) catalysts show higher H₂ conversion activity but with no selectivity for H₂O₂, and also show much higher H₂O₂ decomposition activity. No direct correlation is observed between the H₂-to-H₂O₂ conversion activity (or H₂O₂ selectivity) and the Pd dispersion or surface acidity of the catalysts. Higher H₂O₂ yield and lower H₂O₂ decomposition activity are, however, obtained when the non-acidic reaction medium (water with or without NaCl) is replaced by the acidic one.     

以活性炭纤维为载体的金属氧化物上分解N2O研究

制备了载有K、Fe、Cu、Sr、Mg金属氧化物的活性炭纤维(M/ACF)催化剂,用于N2O分解反应.实验结果表明它们对该反应的活性顺序为K/ACF>Fe/ACF>Cu/ACF>Mg/ACF>Sr/ACF>ACF, 其中K/ACF可在350℃时将N2O完全分解.基于K/ACF特殊的高活性,对该催化剂及空白炭纤维进行了TPD、TG实验,并进一步进行了活性实验.结果表明,N2O在K/ACF上,反应产物中CO2含量明显低于文献中已报导的其它C(NXO脱除反应产物中的CO2含量,其原因在于,对于K/ACF,在K2O活性中心作用下N2O的分解温度明显低于C(O)活性中心作用下炭纤维的氧化温度,在较低的温度范围内(280～330℃),K2O活性中心起主要的活性作用,使得N2O在K/ACF上大量分解, 而C(O)活性中心却没有明显的参与反应,所以CO2的生成量较小.反应前后K/ACF的SEM图样对比也表明经过反应,活性炭纤维表面没有明显的损伤,C(O)活性中心作用并不明显.     

CuO／Ce1-xZrxO2催化分解NO的研究

NO对环境的影响日益严重,如果不有效将其消除掉,将会对环境及人的健康产生极大的危害。因此,目前各国都在研究廉价消除NO污染的方法。采用共沉淀法制备了催化剂CuO／Ce1-xZrxO2,利用XRD对其晶相进行表征,H2-TPR研究了其氧化还原能力,以NO的转化效率作为评价指标。结果表明：适当比例zr的加入以及适当比例的CuO能提高活性。