Hydrogenolysis of hydrocarbons over supported catalysts derived from metal carbonyl clusters

A comparison between the activities of silica-supported ruthenium, rhodium and platinum catalysts prepared from metal cluster compounds and their conventional analogues towards the activation of saturated hydrocarbons has been made. Ruthenium cluster-derived catalysts display greatly enhanced activity for the complete hydrogenolysis of straight chain aliphatic hydrocarbons to methane and provide a temperature advantage of 150°C relative to conventionally prepared ruthenium catalysts where only moderate hydrocarbon conversions are noted. The increased activity superficially correlates with the smaller metal crystallite sizes (15–20 Å) reproducibly obtainable using metal cluster compounds as catalyst precursors. The highly specific activity for the hydrogenolysis of C-C bonds in saturated hydrocarbons has been applied to the selective cleavage of the alkyl group in ethylbenzene, giving toluene and methane. Conversions of up to 30% ethylbenzene have been observed at 225°C and 1 atm using a Ru₃(CO)₁₂/SiO₂-based catalyst. The xylenes, particularly o-xylene, are much less susceptible to hydrogenolysis and, at 225°C, relative hydrocarbon destruction rates of 30 : 1 and 7 : 1 have been observed using mixed feeds of ethylbenzene/o-xylene and ethylbenzene/p-xylene, respectively. Such a catalyst system can, in principle, therefore provide a means of separating ethylbenzene from its mixtures with xylenes.     

Polyaniline-functionalized carbon nanotube supported platinum catalysts

Electrocatalytically active platinum (Pt) nanoparticles on a carbon nanotube (CNT) with enhanced nucleation and stability have been demonstrated through introduction of electron-conducting polyaniline (PANI) to bridge the Pt nanoparticles and CNT walls with the presence of platinum-nitride (Pt-N) bonding and π-π bonding. The Pt colloids were prepared through ethanol reduction under the protection of aniline, the CNT was dispersed well with the existence of aniline in the solution, and aniline was polymerized in the presence of a protonic acid (HCl) and an oxidant (NH(4)S(2)O(8)). The synthesized PANI is found to wrap around the CNT as a result of π-π bonding, and highly dispersed Pt nanoparticles are loaded onto the CNT with narrowly distributed particle sizes ranging from 2.0 to 4.0 nm due to the polymer stabilization and existence of Pt-N bonding. The Pt-PANI/CNT catalysts are electroactive and exhibit excellent electrochemical stability and therefore promise potential applications in proton exchange membrane fuel cells.     

Preparation of supported platinum catalysts from tetrakis (Triphenylphosphine) platinum by impregnation

Pt[P(C₆H₅)₃]₄ has been applied for preparation of Pt/C and Pt/Al₂O₃ catalysts. The highest hydrogenation activity exhibited the catalysts prepared using alumina support. Activity of these catalysts is higher compared with those obtained from Pt(NH₃)₄Cl₂.

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Pt[P(C₆H₅)₃]₄ Pt/C Pt/Al₂O₃. , , . , Pt(NH₃)₄Cl₂.

     

Hydrodechlorination of chloroalkanes on supported platinum catalysts

Summary  Vezetéknév     

Silylation of porous glass supported platinum catalysts

Effect of silylation with hexamethyldisilazane on adsorption and catalytic properties of porous glass-supported platinum catalysts has been studied. Catalytic activity decreases markedly with an increase in surface coverage by trimethylsilyl groups for all the following reactions examined: hydrogenation of benzene, dehydrogenation of cyclohexane and dehydrocyclization of n-hexane.

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, . , : , -.

     

Dendrimer-encapsulated nanoparticle precursors to supported platinum catalysts

In this contribution, we report the successful preparation of supported metal catalysts using dendrimer-encapsulated Pt nanoparticles as metal precursors. Polyamidoamine (PAMAM) dendrimers were first used to template and stabilize Pt nanoparticles prepared in solution. These dendrimer-encapsulated nanoparticles were then deposited onto a commercial high surface area silica support and thermally activated to remove the organic dendrimer. The resulting materials are active oxidation and hydrogenation catalysts. The effects of catalyst preparation and activation on activity for toluene hydrogenation and CO oxidation catalysis are discussed.     

Molecular simulation of oxygen on supported platinum clusters

Molecular dynamics simulations are performed to study oxygen adsorption on platinum clusters supported on a graphite surface. The Sutton–Chen many-body potential is used for the Pt–Pt interaction, whereas a Steele potential was used to represent the carbon surface. The oxygen–oxygen intramolecular force is modeled by a harmonic oscillator model and other interactions are described by the Lennard–Jones potential. The results indicate an optimum loading of platinum for maximum specific adsorption of oxygen. Adsorption isotherms are constructed and the energies and orientation of adsorbed oxygen are reported. The relevance of this study to electrode processes is discussed.     

Partial hydrogenation of benzene over platinum supported catalysts

Partial hydrogenation of benzene to cyclohexene has been studied on Pt/Nylon 66, Pt/MgO and Pt/TiO₂. An effect of the support on the selectivity to cyclohexene was observed, Pt/Nylon showing the highest selectivity, followed by Pt/MgO and Pt/TiO₂. An interaction of platinum with the more basic supports (Nylon, MgO) and a pretreatment under oxidizing conditions, results in a higher selectivity to cyclohexene.

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Pt/ 66, Pt/MgO PtTiO₂. , Pt/, Pt/MgO Pt/T,O₂. (, MgO) .

     

Carbon monoxide hydrocondensation on iron catalysts prepared from metal carbonyl compounds

The iron/alumina catalysts prepared by the impregnation of Fe(CO)₅ on the support have properties quite different from those of the conventional catalysts in the CO+H₂ reaction. However, the preparation procedure or the activation of the solid has a decisive effect on the activity, selectivity and stability.

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Fe(CO)₅ , , CO+H₂. , , .

     

Some aspects of reversible chemisorption on supported platinum catalysts

Hydrogen and carbon monoxide chemisorption on supported platinum catalysts have been studied volumetrically and the adsorption heats determined by microcalorimetric measurements. From the results of this study is concluded that the use of reversible (or second) isotherms as a measure of weak chemisorption would appear inadequate.     

Specific properties of dehydrogenation centers in supported platinum catalysts

Cyclohexane dehydrogenation was used as a model reaction to study the dehydrogenation function of Pt/Al₂O₃ catalysts. Fresh and coked catalysts were tested in two ranges of reaction conditions: model conditions (T=280–340°C, P=1 atm) and the conditions used in the naphtha reforming process (T=420–460°C, P=15 atm). Intrinsic properties of the dehydrogenation active centers were found to be identical throughout the experimental conditions. The coke deposits only block a part of the active centers without their qualitative modification.     

Model catalysts of supported Au nanoparticles and mass-selected clusters

In surface science, much effort has gone into obtaining a deeper understanding of the size-selectivity of nanocatalysts. In this article, electronic and chemical properties of various model catalysts consisting of Au are reported. Au supported by oxide surfaces becomes inert towards chemisorption and oxidation as the particle size became smaller than a critical size (2-3 nm). The inertness of these small Au nanoparticles is due to the electron-deficient nature of smaller Au nanoparticles, which is a result of metal-substrate charge transfer. Properties of Au clusters smaller than ～20 atoms were shown to be non-scalable, i.e., every atom can drastically change the chemical properties of the clusters. Moreover, clusters with the same size can show dissimilar properties on various substrates. These recent endeavours show that the activity of a catalyst can be tuned by varying the substrate or by varying the cluster size on an atom-by-atom basis.     

低温水热法制备硅胶负载型二氧化钛催化剂

TiO2作为一种优良的光催化材料,能够降解有机物,起到抗菌防污的作用,其在工业上的潜在应用已吸引众多研究者的普遍关注和深入研究[1-3]。为了进一步提高它的光催化活性,研究者试图运用各种方法和技术对纯TiO2进行改进。负载[3]是其中常用方法之一。对于无负载的二氧化钛,由于本     

Synthesis and some properties of heteronuclear platinum and palladium carbonyl clusters

Heteronuclear clusters of general formula [Pt_xPd_y(CO) _z] were synthesized by reaction of CO with PtCl₄ + PdCl₂ solutions in 95% ethanol at room temperature and atmospheric pressure. The products isolated were analyzed by IR spectroscopy, thermogravimetry, and X-ray powder diffraction.     

Study of the local structure of supported nanostructural platinum catalysts

The possibility of controlling the state of platinum deposited on the support surface via minor changes in the catalyst preparation procedure is demonstrated using a series of highly dispersed Pt/γ-Al₂O₃ catalysts with different particle size of the active component. Dispersity, local structure and electronic state of supported platinum were examined by a combination of high resolution transmission electron microscopy and X-ray absorption spectroscopy (EXAFS/XANES). It was shown that various platinum species can be obtained on the surface of the support: bulk or surface Pt(II) or Pt(IV) oxides, mixed metal-oxide structures, bulk particles of metallic platinum, and two-dimensional surface Pt⁰ particles strongly interacting with the support.     

Synthesis, characterization, and testing of supported Au catalysts prepared from atomically-tailored Au38(SC12H25)24 clusters

Nearly monodispersed Au(38)(SC(12)H(25))(24) clusters (1.7 ± 0.2 nm) were synthesized using a modified Brust process while utilizing a "thiol etching" approach for the ligand exchange. HRTEM, MALDI, FTIR, and XAS analysis confirmed the formation of the 38-atom clusters in solution. This solution was used to impregnate a microporous TiO(2) support to give 0.7% Au(38)/TiO(2) catalyst. Subsequent drying in air and treatment with H(2)/He at 400 °C removed most of the sulfur ligands, and also increased the Au cluster size to 3.9 ± 0.96 nm. XPS and EXAFS analysis of this supported catalyst showed trace levels of residual sulfides, apparently located at the Au-TiO(2) interface. CO oxidation tests on these supported clusters show an activation energy and range of TOFs comparable to those reported by others. These results suggest that supported Au clusters of controllable size can be prepared with this thiol-ligated solution-based method, providing a new approach to the synthesis of these catalysts.     

Thermal characterisation of alumina supported chromium and platinum–chromium catalysts

This study presented results on reduction of alumina supported chromium and platinum–chromium catalysts using temperature programmed reduction method (TPR). It has been shown that catalysts after earlier oxidation step but without calcinations one undergo reduction in lower temperature in comparison to calcined only catalysts. Moreover, addition platinum to Cr/Al₂O₃ catalysts also caused decrease of reduction temperature. It has been observed that over the examined catalysts oxidation CO to CO₂ and reduction CO to CH₄ occurs. However, on Pt–Cr catalysts both reactions proceed at lower temperature compare to Cr catalysts.     

应用于氧还原反应的石墨烯-无定形碳核壳结构复合材料载铂催化剂(英文)

采用氯化法制备石墨烯-无定型碳复合材料(GNS@a-C),并用作质子交换膜燃料电池(PEMFC)氧还原反应Pt催化剂的载体.结果显示,所制Pt/GNS@a-C催化剂与传统商业催化剂Pt/C相比,有较好的活性和较高的稳定性:质量活性(0.121 A/mg)几乎是Pt/C(0.064 A/mg)的两倍.更重要的是,该新型催化剂加速4000圈后其电化学活性面积保留了最初的51%,与Pt/C的33%相比,前者有更好的电化学稳定性,显示它在PEMFC中将具有较好的应用潜力.     

γ-Radiation produced supported metal complex catalysts : II. Cobalt carbonyl hydroformylation catalysts supported on polypropylene containing pyridine side chains

The optimum conditions necessary to prepare novel polymer supports for use in catalysis by the γ-radiation grafting of 4-vinylpyridine on to polypropylene are shown to be a total dose of 2 Mrad at a dose rate of 300 Krad h^?1 using a monomer to polymer ratio of 40 per cent mol/mol. Addition of 0.1 per cent w/v of p-tert-butylcatechol increases the grafting yield almost two fold. Comparison of the hydroformylation of 1-hexene in the presence of cobalt carbonyl supported on 4-vinylpyridine grafted on to polypropylene shows an increase in specificity, as determined by the ratio of normal/branched heptanal formed, by a factor of about 2.5 over the corresponding homogeneous catalyst. The supported system is of similar activity to the homogeneous system. The greater specificity of the supported catalyst is ascribed to the total environment surrounding the catalytically active site in which both the pyridine sidechain and the polypropylene backbone are believed to play an important role.