The Distribution of Active ingredients in Supported Catalysts Prepared by Impregnation

Supported catalysts, one of the commonest forms of heterogeneous catalysts in practical use, consist of small crystallites of a catalytically active component dispersed in a porous support of high surface area. Impregnation of the support with an aqueous solution of a compound containing the appropriate catalytic component is an important and frequently used method of preparing this type of catalyst. A nonaqueous solution should be used if the sup port surface is hydrophobic or if hydrolysis of the support surface is to be avoided. In its simplest form, this impregnation method involves three steps: (1) contacting the support with impregnating solution for a certain period of time, (2) drying the support to remove the imbibed liquid, and (3) activating the catalyst by calcination, reduction, or other appropriate treatment.     

Dispersion and Distribution of Ruthenium on Carbon-Coated Ceramic Monolithic Catalysts Prepared by Impregnation

Carbon-coated monolithic catalysts were prepared by dipcoating a cordierite substrate in a Furan resin, after which the ruthenium was incorporated by impregnation with a [RuCl₅]^2- complex. Immobilization of the precursor proceeded particularly via weak physisorption. Since the carbon-coated monolithic supports have a broad pore-size distribution, redistribution of the ruthenium precursor occurred upon drying due to capillary forces, resulting in low dispersion. A significant amount of ruthenium is present on the surface of the carbon inclusions located deep in the cordierite walls, making the diffusion path of the reactants to the active ruthenium sites considerably larger than the average carbon-coating thickness. For successful application of the carbon-coated monolithic catalysts in gas–liquid reactions, the deposition of carbon in the walls of the monolith should be prevented and maldistribution of ruthenium upon drying should be solved.     

Synthesis of Supported Catalysts by Impregnation and Calcination of Low-Temperature Polymerizable Metal-Complexes

The low-temperature polymerizable metal complex solution has been used as an active component precursor to prepare supported (structured) catalysts by a straight-forward sequence of impregnation, drying and calcination. Two typical samples, 5 wt% Zr _x Ce_1?x O₂/Al₂O₃ nanocomposite and structured carbon nanofiber supported Cu?CCeO₂ catalyst, are prepared to explore the potential of this method in the controlled synthesis of catalysts and catalyst supports. The interaction between the active component precursor and the surface of the solid matrices during impregnation and drying is investigated by infrared spectroscopy (IR) and transmission electron microscopy (TEM), demonstrating that the in situ polymerization process is crucial for the deposition of the active component on the surface of solid matrices. The evolution of the phase transformation and the structure of the produced materials during the calcination step is studied by coupling thermal gravimetric analysis?Cdifferential thermal analysis?Cmass spectroscopy (TGA?CDTA?CMS), TEM and X-ray diffraction (XRD) measurements, indicating that higher thermal stable particles or smaller particles can be obtained with the presence of the Al₂O₃ or structured carbon nanofibers (SCNF), respectively, after calcination. This method combines the advantages of sol?Cgel and impregnation, representing a promising route for preparing supported catalysts and catalyst supports. The limitations of the method are also discussed.     

TiO2 Supported Nano-Au Catalysts Prepared Via Solvated Metal Atom Impregnation for Low–Temperature CO Oxidation

The Ce _x Ti_1?x O₂ mixed oxides at different mole ratios (x=0.1–1.0) were prepared by co-precipitation of TiCl₄ and Ce(NO₃)₃. The structural and reductive properties of the Ce _x Ti_{1? x} O₂ were affected by calcination temperature. At x=0.1–0.3, CeTi₂O₆ phase was formed and mainly as amorphous after calcination at 650°C. At x=0.3, only CeTi₂O₆ was formed after calcination at 750°C and CeTi₂O₆ crystallized completely after calcination at 800°C. TPR analyses showed that the amount of H₂ consumption by Ce _x Ti_1?xO₂ (650°C) (except x=0.1) was greater than that by single CeO₂, and the valence of CeO₂was the lowest (+3.18) at x=0.3. CuO/Ce_0.3Ti_0.7O₂ was prepared by the impregnation method and catalytic properties were examined by means of a GC micro-reactor NO+CO reaction system, BET, TPR, XRD, XPS and NO-TPD. It was found that CuO/Ce_0.3Ti_0.7O₂ calcined at 650°C had the highest activity in NO+CO reaction with 100% NO conversion at reaction temperature of 300°C, and at 650°C Ce_0.3Ti_0.7O₂just began to crystallize. The catalytic activities were largely affected by the pre-treatment conditions. At low reduction temperature (100°C), CuO species was difficult to reduce. When high degree of reductions took place, both CuO species and Ce_0.3Ti_0.7O₂ reduced and thus a part of CuO species on the support surface would be covered. The XPS and NO-TPD analyses showed that CuO/Ce_0.3Ti_0.7O₂ had four NO absorption centers (Cu⁺, Cu²⁺(I), Cu²⁺(II) and Ce³⁺). The CuO species involving in NO+CO reaction included Cu²⁺(I) and Cu⁺, and CeO₂ species (Ce³⁺ and Ce⁴⁺).     

TiO2 Supported Nano—Au Catalysts Prepared via Solvated Metal Atom Impregnation for Low-Temperature CO Oxidation

TiO₂ supported nano-Au catalysts were prepared by solvated metal atom impregnation (SMAI) method. The catalysts were characterized by means of AAS, TPD, H₂ reduction desorption (H₂-RD), XRD, TEM, XPS and tested for low-temperature CO oxidation. XRD and TEM results showed that the pretreatment temperature had an influence on the particle size of Au/TiO₂catalysts. The average particle size increased with the increase in pretreatment temperature. XPS indicated that gold in the catalysts was presented in the form of metallic state clusters. Catalytic studies showed these catalysts were very active and stable in low-temperature CO oxidation. The CO oxidation activity of the catalysts increased as the Au particle size decreased. The measurement results of AAS, TPD and H₂-RD revealed that there were some organic fragments on the surface of Au particles which might be responsible for the high stability of the Au/TiO₂ catalysts.     

Tungsten-Ferrierite Catalysts Prepared by Impregnation and Ion-Exchange: Characterization and Activity During the Skeletal Isomerization of Linear Butenes

Tungsten-ferrierite catalysts were prepared by impregnation and ion-exchange. Potassium (KF), ammonium (AF), and protonic (HF) ferrierites were used as starting materials. Characterization of impregnated catalysts shows reduction peaks characteristic of tungsten species, whereas the absence of a peak in the corresponding profiles of the exchanged material indicates such species were incorporated into the framework. For impregnated materials, the tungsten species-surface interaction is not strong. Catalytic performance during the linear butene skeletal isomerization at 300 °C and at atmospheric pressure was measured. Exchanged materials reach both conversion and isobutene yield larger than the impregnated ones. Samples prepared from AF and HF practically display the same catalytic behavior at 5 min, being associated with the presence of strong acid sites. Tungsten-impregnated KF does not reach a high activity at a short time-on-stream (TOS), showing a particular by-product distribution related to the absence of strong acid sites. Even though exchanged samples starting from KF show the HF characteristic behavior, differences at 5 min appear. By-product distributions allow us to consider their formation from dimers and/or oligomers. At 5 min, the C₅ ⁺ fraction is the main one, following propene, propane, and butane in similar proportions. Over the clean surface, propene could be involved in other reactions considering its high reactivity. At a long TOS, both the C₅ ⁺ fraction and propane decrease, whereas propene increases, verifying the bimolecular mechanism.     

用溶剂化金属原子浸渍法制备的高分散负载型催化剂Pd－Cu／C的结构与性质

应用溶剂化金属原子浸渍（ＳＭＡＩ）法制备了三种金属含量比不同的Ｐｄ－Ｃｕ／Ｃ双金属催化剂。经ＸＲＤ和ＴＥＭ测定结果表明，催化剂中Ｐｄ和Ｃｕ已形成合金，合金颗粒平均直径小于５ｎｍ。ＸＰＳ和Ａｕｇｅｒ谱说明Ｐｄ和Ｃｕ均以零价态存在。在亚异丙基丙酮（ＣＨ＿３）＿２Ｃ＝ＣＨＣＯＣＨ＿３加氢反应中，随着催化剂中Ｃｕ比例增加，催化活性增大，而生成六碳酮的选择性基本不变。     

The Sintering of Supported Metal Catalysts

Metal catalysts are commonly employed in the form of metal dispersed as small crystallites on high surface area supports. The use of these supported metal catalysts increases the utilization of the metal as a catalyst since a large fraction of the metal atoms are at the surface of the small metal crystallites. Another important function of the support is to physically separate the small metal crystallites and thereby hinder the agglomeration of the small metal crystallites into larger crystallites. This agglomeration would decrease the number of surface metal atoms per unit mass of metal, and thereby decrease the utilization of the metal and the activity of the catalyst.     

Methanol Decomposition to Synthesis Gas Over Supported Pd Catalysts Prepared from Hydrotalcite Precursors

Supported Pd catalysts were prepared by solid-phase crystallization (spc) starting from MgAl hydrotalcite anionic clay minerals as the precursors, and were tested for the methanol decomposition to synthesis gas. The precursors based on [Mg₆Al₂(OH)₁₆CO₃ ^2-] · 4H₂O were prepared by coprecipitation from raw materials containing Pd²⁺, Mg²⁺ and Al³⁺ ions as the components of hydrotalcite. The precursors were thermally decomposed and reduced to afford supported Pd catalysts on MgAl mixed oxide. Pd-supported catalysts as a reference were also prepared by the impregnation (imp) method. The spc-Pd catalysts thus prepared afforded highly dispersed Pd metal particles and showed higher activity as well as lower activation energy than the imp-Pd catalysts. When the precursor was prepared under mild conditions, finer particles of Pd metal were formed over the catalyst, resulting in a high activity. In the case of spc-Pd catalysts, carbon monoxide adsorbed on Pd easily desorbed, compared with imp-Pd catalysts. It is likely that the high activity is due to the highly dispersed and stable Pd metal particles and the easy desorption of carbon monoxide.     

负载型非茂金属催化剂聚合制备UHMWPE

在淤浆聚合条件下采用新型负载型非茂金属催化剂(SSTU)制备了超高相对分子质量聚乙烯(UHMWPE),考察了聚合温度、预聚合、助催化剂用量等聚合条件对催化剂活性、UHMWPE堆密度、粒径分布、粘均相对分子质量、力学性能、结晶性能和微观形貌等的影响.结果表明,提高聚合温度和助催化剂用量有利于催化剂活性发挥,而降低聚合温度和不预络合时可以得到高粘均相对分子质量的UHMWPE.由SSTU聚合得到的UHMWPE粒径分布均匀,细粉含量低(质量分数小于0.5%),结晶性能和力学性能好,在微观形貌上与齐格勒-纳塔催化剂制备的UHMWPE有显著区别.     

Highly Active Silica Gel‐Supported Metathesis (Pre)Catalysts

Highly active Hoveyda–Grubbs and Hoveyda–Blechert type (pre)catalysts, immobilized on silica gel, are presented. These (pre)catalysts are synthesized in a few steps from readily available precursors and demonstrate high activity in a number of test metathesis reactions. The catalyst is easily separated by simple filtration of the non‐swelling material.     

Preparation of MoO3/Al2O3 Catalysts with Sharp Eggshell Mo Distribution by Slurry Impregnation

MoO₃/Al₂O₃ catalysts with eggshell Mo concentration profiles were prepared by reaction of Al₂O₃ extrudates or balls with slurry of MoO₃ in water. The Mo concentration wave penetrating Al₂O₃ particles during this slurry impregnation was almost rectangular. Its height was close to the filled monolayer loading. The thickness of the shell was regulated either by impregnation time or by the MoO₃ amount in the slurry. The hydrodesulfurization activity of Mo species deposited by slurry impregnation was about the same or better (depending on the Al₂O₃ used) as in industrial MoO₃/Al₂O₃ catalyst.     

浸渍法制备Pt/Al_2O_3催化剂的研究——竞争吸附剂对Pt分布的影响

水溶液中有机酸在η-Al_2O_3上的饱和吸附量（x/m）_M依下列顺序增大:乙酸<一氯乙酸<乳酸<酒石酸<柠檬酸。用H_2PtCl_6溶液浸渍η-Al_2O_3时,若以上述有机酸为竞争吸附剂,则（x/m）_M越大者将使H_2PtCl_6平衡吸附量下降越多。浸渍动力学的研究表明,在竞争吸附剂存在时,H_2PtCl_6在η-Al_2O_3载体上的吸附量取决于吸附平衡。柠檬酸、酒石酸可使H_2PtCl_6平衡吸附量大为下降,这是它们使Pt可能形成蛋白型分布的原因。另外三种酸使H_2PtCl_6平衡吸附量下降不大,因而不能使Pt呈蛋白型分布。     

茂金属催化剂负载化及负载机理的研究进展

总结了茂金属催化剂负载化、栽体种类和负载方法,评述了茂金属催化剂负载机理的研究方法和研究状况。指出将实验方法和计算机分子模拟方法二者结合起来,能够加快研究进程。     

The Selective Oxidation of 1,2-Propanediol by Supported Gold-Based Nanoparticulate Catalysts

The oxidation of 1,2-propanediol to form lactic acid and hydroxyacetone has been investigated using supported metal nanoparticles. A series of supported gold, palladium, platinum and combinations of these metals have been investigated. In the presence of base the major product formed is lactate, often in excellent yields as, under these conditions the terminal hydroxyl group is oxidised. In the absence of base, more vigorous conditions are required to elicit high conversions; surprisingly, a major product from such reactions is a mono-oxidation product hydroxyacetone, along with lactate.     

Synthesis of Supported Catalysts by Atomic Layer Deposition

A promising new method of catalyst synthesis is atomic layer deposition (ALD). ALD is a variation on chemical vapor deposition wherein metals, oxides and other materials are deposited on surfaces via a sequence (usually binary) of self-limiting reactions. The self-limiting character of the reactions makes it possible to achieve uniform deposits on high-surface-area porous solids and, hence, produce practical catalytic materials. The ability to deposit uniform layers in a sequence makes it possible to fabricate the support and then construct the catalytic metal and/or metal oxide species and add modifier layers in any desired order. This article will provide a short introduction to the technique of ALD and its application to the synthesis of supported catalytic metal nanoparticles and oxide monolayers.     

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。     

溶胶-凝胶法制备纳米尺度催化剂的研究进展

介绍了溶胶-凝胶法制备纳米尺度催化剂的基本过程和其最新研究进展。指出:将溶胶-凝胶法与其他技术相结合,从而提高纳米催化剂的稳定性,将是溶胶-凝胶法在纳米催化剂制备中的发展方向。     

无配体负载钯催化Suzuki偶联反应的研究进展

金属钯催化的Suzuki偶联反应是碳一碳偶联反应中的最重要的反应之一。传统的均相催化体系具有很多的不足,如产物与催化剂不易分离、原料价格昂贵、催化剂不能重复使用等,而使用无配体负载钯的催化剂可有效地解决上述问题。综述了近些年来无配体材料负载钯催化Suzuki偶联反应的研究进展,载体包括碳材料、多孔分子筛、水滑石、高分子材料、金属氧化物、硅藻土、纤维素、磷灰石和氟硅胶等。