One-step pyrolysis process to synthesize dispersed Pt/carbon hollow nanospheres catalysts for electrocatalysis

An effective method for loading Pt nanoparticles on monodispersed hollow carbon nanospheres by one-step pyrolysis of polystyrene spheres (PS) adsorbed with platinum (IV) ions was developed. The polystyrene spheres were firstly enwrapped with a layer of sucrose and cetyltrimethyl ammonium bromide (CTAB) micelles. Adsorption of platinum (IV) ions onto the polystyrene spheres was carried out via electrostatic interaction between the negatively charged platinum salt and the positively charged amino group in the CTAB. Pyrolysis of the PS-Pt (IV) precursors at 600 °C under nitrogen atmosphere resulted in the simultaneous decomposition of the sucrose to carbon and the adsorbed platinum complex to metallic Pt. During this process the polystyrene spheres was removed and hollow sphere of PtC formed. Nanocomposites of hollow carbon nanospheres with different platinum loading were synthesized and their electrocatalytic activity was evaluated using methanol as a model molecule. Results showed that the as-prepared hollow carbon nanospheres supported platinum catalysts have high electrocatalytic activity and long-term stability towards the oxidation of methanol. The present method is promising for the fabrication of carbon supported platinum catalysts for the direct methanol fuel cell.     

Characterization of Pt-Ru/C catalysts by X-ray absorption spectroscopy and temperature-programmed surface reaction

X-ray absorption spectroscopy (XAS) was employed to characterize carbon black supported Pt-Ru catalysts, which are commercially available to be utilized as the anode of polymeric-electrolyte-membrane fuel cells. Both Pt and Ru were found partially oxidized in the as-received form. Upon exposure to hydrogen at room temperature, the catalysts were completely reduced to the metallic state. The bimetallic nanoparticles on the Pt-Ru/C catalysts possess an inner core enriched in Pt, which is surrounded by a Ru-rich outer shell. Such a core–shell structure retained even at an elevated reduction temperature of 623 K. Temperature-programmed surface reaction (TPSR) was carried out to explore the reactivity of adsorbed CO toward hydrogen on various catalysts. Both the peak temperature of the TPSR profile and the amount of methane generated during the course of TPSR were sensitive to the surface composition of Pt–Ru nanoparticles. In combination of XAS and TPSR results, a slight difference in the nanostructure between two Pt-Ru/C catalysts was manifested.     

Mechanochemical synthesis of highly dispersed iron oxide from metallic powders in manufacture of catalysts

X-ray phase, X-ray diffraction, and synchronous thermal analyses, Mossbauer and IR spectroscopy, and scanning electron microscopy were used to study processes occurring in the stages of mechanochemical oxidation and thermal treatment of coarsely dispersed iron and cast iron powders in a dispersion medium of water and oxalic acid solutions. The optimal mechanochemical-synthesis conditions were determined and it was found that the preparation method affects the phase composition, structure, and properties of the resulting oxides. It was experimentally confirmed that the mechanochemical oxidation method makes it possible to obtain oxides by the zero-sewage technology with a specific surface area 1.5–12 times larger that that in oxides produced by the conventional precipitation technique. An analysis of the reactivity of the samples in the model reaction of carbon monoxide conversion by steam demonstrated their high catalytic activity.     

Synthesis of cis-vinyltrimethylstannanes and cis-vinylpinacolboronates in a two-step highly regio and stereoselective process

A highly efficient two-step regio and stereoselective method for the synthesis of both cis-vinyltrimethylstannanes and cis-vinylpinacolboronates is described. This method takes advantage of the known lithium/tellurium exchange pathway providing a versatile alternative to known literature methods. The methodology presented demonstrates compatibility, for example, with substrates bearing oxygen functionality in comparison to previously reported methods of cis-selective hydrostannylation (i.e., ZrCl₄).     

Ethanol electrocatalytic oxidation on highly dispersed Pt-TiO<Subscript>2</Subscript>/C catalysts

Carbon supported Pt-TiO₂(Pt-TiO₂/C) catalysts were prepared with colloidal and chemical reduction method on different conditions and used for ethanol electrooxidation in acidic solution. The size of TiO₂ and Pt crystal varied on the catalysts prepared by different methods and the Electrochemical specific surface area (ESA) also showed different on these catalysts. The catalytic activity on these carbon supported Pt-TiO₂ catalysts showed some different behaviors. Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 7, pp. 785–790. The article is published in the original.     

New possibilities for preparation of highly dispersed PtFe/SiO2 catalysts

Pt(CH₃)₃Cl complex has been applied for preparation of highly dispersed Pt/SiO₂ catalyst. Iron in different forms was used as second component for PtFe/SiO₂ catalyst. Dispersity of Pt is comparable to that obtained via Pt(NH₃) ₄ ²⁺ exchange. Catalytic activity and isomerization are explained in terms of Fe blocking of the surface.

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Pt(CH₃)₃Cl Pt/SiO₂. PtFe/SiO₂. Pt(NH₃) ₄ ⁺² . .

     

Facile synthesis of perfluoroalkylated fluorenes via a one-pot two-step three-component process

The efficient synthesis of perfluoroalkyl-substituted fluorenes directly from indenones, malononitrile and methyl perfluoroalk-2-ynoates via a one-pot two-step three-component cascade process is reported. Up to 12 examples of indenones with various substituents were converted into their corresponding functionalized fluorene derivatives in good to excellent yields.     

Simple and highly efficient synthesis of oxaziridines by tetrabutylammonium Oxone

Oxygenation of various aldimines with tetrabutylammonium monoperoxysulfate produced the corresponding E- or a mixture of E- and Z-oxaziridines with very high yields (?90%) and good to excellent selectivities (75-100%) within 20 min to 10 h in CH₃CN at room temperature (∼25 °C). The E/Z isomer ratio critically depends on the stereo-electronic nature of the substituents in the oxaziridines, solvent, and the presence of Lewis acids and bases.     

Surface structure and reaction performances of highly dispersed and supported bimetallic catalysts

Surface structures of Pt-Sn and Pt-Fe bimetallic catalysts have been investigated by means of Mssbauer spectroscopy, Pt-L_Ⅲ-edge EXAFS and H_2-adsorption. The results showed that the second component, such as Sn or Fe, remained in the oxidative state and dispersed on the γ-Al_2O_3 surface after reduction, while Pt was completely reduced to the metallic state and dispersed on either the metal oxide surface or the γ-Al_2O_3 surface. By correlating the distribution of Pt species on different surfaces with the reaction and adsorption performances, it is proposed that two kinds of active Pt species existed on the surfaces of both catalysts, named M_1 sites and M_2 sites. M_1 sites are the sites in which Pt directly anchored on the γ-Al_2O_3 surface, while M_2 sites are those in which Pt anchored on the metal oxide surface. M_1 sites are favorable for low temperature H_2 adsorption, and responsible for the hydrogenolysis reaction and carbon deposition, while M_2 sites which adsorb more H_2 at higher tem     

Preparation and characterization of nano-sized Pt-Ru/C catalysts and their superior catalytic activities for methanol and ethanol oxidation

Carbon-supported PtRu nanoparticles (Ru/Pt: 0.25) were prepared by three different methods; simultaneous reduction of PtCl(4) and RuCl(3) (catalyst I) and changing the reduction order of PtCl(4) and RuCl(3) (catalysts II and III) to enhance the performance of the anodic catalysts for methanol and ethanol oxidation. Structure, microstructure and surface characterizations of all the catalysts were carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results of the XRD analysis showed that all catalysts had a face-centered cubic (fcc) structure with different and smaller lattice parameters than that of pure platinum, showing that the Ru incorporates into the Pt fcc structure by different ratios in all the catalysts. The typical particle sizes of all catalysts were in the range of 2-3 nm. The most active and stable catalyst for methanol and ethanol oxidation is catalyst III, in which a large amount (more than 90%) of PtRu alloy formation was observed. It has been found that this catalyst is about 8.0 and 33.4 times more active at ～0.60 V towards the methanol and ethanol oxidation reactions, respectively, compared to the commercial Pt catalyst.     

Hydrothermal synthesis and photocatalytic activity of highly dispersed ZnO powders

The micromorphology of highly dispersed ZnO powders formed from Zn(OH)₂ gels under hydrothermal conditions is studied by powder X-ray diffraction, X-ray diffraction analysis, and low-temperature nitrogen adsorption. The parameters of hydrothermal synthesis (heating rate, treatment duration, and temperature) are found to effect the microstructural characteristics of the products. The photocatalytic activity of the synthesized zinc oxide samples in the model reaction of Methyl Orange photodegradation is studied. The synthesis parameters for preparing ZnO powders with high photocatalytic activity are determined.     

A new two-step four-component synthesis of highly functionalized cyclohexenols by sequential nickel-catalyzed couplings

A new two-step procedure for the synthesis of cyclohexenols has been developed. A nickel-catalyzed three-component addition of an enal, alkyne, and acetylenic tin affords substituted hept-4-en-6-ynals. The products of this first step then undergo a second nickel-catalyzed reaction with organozincs or organoboranes to afford densely functionalized cyclohexenols. Variation in each of the four components is tolerated to provide access to a wide range of versatile building blocks.     

Facile synthesis of highly dispersed palladium/polypyrrole nanocapsules for catalytic reduction of p-nitrophenol

In this study, a facile one-step redox polymerization method for the preparation of highly dispersed palladium (Pd)/polypyrrole (PPy) nanocapsules has been demonstrated. During the polymerizaion process, the formation of RB-PdCl(4)(2-) complex via an electrostatic interaction plays a key role for the preparation of Pd/PPy composite nanocapsules. The well-dispersed Pd nanocrystals with small sizes of 2-4 nm embedded in PPy nanocapsules exhibited a good catalytic activity during the catalytic reduction of p-nitrophenol into p-aminophenol by NaBH(4) in aqueous solution. The kinetic apparent rate constant (k(app)) was about 8.87×10(-3) s(-1). Moreover, the as-prepared Pd/PPy composite nanocapsules exhibited a good reusability, which could be repeatedly used for the reduction of p-nitrophenol with a high catalytic activity for at least 10 successive cycles.     

Ultrasonic assisted polyol synthesis of highly dispersed Pt/MWCNT electrocatalyst for methanol oxidation

A novel chemical method based on ultrasonic assisted polyol synthesis for the fabrication of highly dispersed Pt nanoparticles on multi-walled carbon nanotubes (MWCNTs) was developed. The simple and green method took only about 10 min at ambient temperature. The structure and chemical nature of the resulting Pt/MWCNT composites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive X-ray spectrometry (EDS). The results showed that the prepared Pt nanoparticles were uniformly dispersed on the MWCNT surface. The mean size of Pt nanoparticles was about 2.8 nm. Electrochemical properties of Pt/MWCNT electrode for methanol oxidation were examined by cyclic voltammetry (CV) and excellent electrocatalytic activities could be observed. The possible formation mechanism of Pt/MWCNTs was also discussed.     

The facile synthesis of benzothiazolylideneacetates and 1,4-benzothiazines through a highly controllable oxidation of benzothiazolylacetates

The synthesis of benzothiazolylideneacetates and 1,4-benzothiazine was found to be highly controllable via simple exchange of corresponding oxidants. It turned out that the treatment of benzothiazolylacetates with m-CPBA gave 1,4-benzothiazines via oxidative ring expansion process, and with DDQ gave benzothiazolylideneacetates via dehydrogenation, in good yield, respectively. The structures of both skeletons were confirmed by their X-ray diffractions. A previously reported method for the synthesis of benzothiazolylideneacetates was thus proved to be incorrect.     

Simple yttrium salts as highly active and controlled catalysts for the atom-efficient synthesis of high molecular weight polyesters

The ring-opening copolymerization (ROCOP) of epoxides and cyclic anhydrides is a promising route to sustainable aliphatic polyesters with diverse mechanical and thermal properties. Here, simple yttrium chloride salts (YCl₃THF_3.5 and YCl₃·6H₂O), in combination with a bis(triphenylphosphoranylidene)ammonium chloride [PPN]Cl cocatalyst, are used as efficient and controlled catalysts for ten epoxide and anhydride combinations. In comparison to past literature, this simple salt system exhibits competitive turn-over frequencies (TOFs) for most monomer pairs. Despite no supporting ligand framework, these salts provide excellent control of dispersity, with suppression of side reactions. Using these catalysts, the highest molecular weight reported to date (302.2 kDa) has been obtained with a monosubstituted epoxide and tricyclic anhydride. These data indicate that excellent molecular weight control and suppression of side reactions for ROCOP of epoxides and cyclic anhydrides can coincide with high activity using a simple catalytic system, warranting further research in working towards industrial viability.

Two simple yttrium salts, YCl₃THF_3.5 and YCl₃·6H₂O, are highly active and controlled catalysts for the perfectly alternating ring-opening copolymerization of epoxides and cyclic anhydrides.     

The controllable synthesis of porous MoN nanorods/carbon for highly efficient electrochemical hydrogen evolution

MoN is a promising material for electrochemical hydrogen evolution due to its cheap price and excellent catalytic activity sites, but the low conductivity prevents further improvement of its catalytic performance. In this work, porous MoN nanorods have been fabricated with an efficient and facile precursor method. XRD, Raman and TEM showed MoN nanorods with diameters of about 100 nm. With a simple mechanical mixing method, MoN/conductive carbon black (CB) composites with different weight ratios have been fabricated. The composite possessed two merits, that is, the more catalytic active site in MoN nanorods due to the porous structure, and fast electron transfer due to the CB. So, it has been used as a hydrogen evolution material. With the proper weight ratio, the composite exhibited brilliant catalytic activity and durability in acidic media. It possesses an overpotential of 162 mV to approach 10 mA cm^?2, a small Tefel slope of 54 mV dec^?1 and maintains the good electrocatalytic activity for at least 10 h. Cyclic voltammetry and electrochemical impedance spectroscopy indicated that the electrocatalyst possessed a high catalytic active area and fast electron transfer. These results can compare with many other recently reported nitride catalysts. Our work possibly provides a new avenue for the preparation of a MoN-based catalyst for highly efficient electrochemical hydrogen evolution.     

高分散加氢脱硫催化剂制备及其对二苯并噻吩的催化性能

近年来,柴油发动机产生的废气污染已成为一个严重问题,环境法规对燃油中的硫含量限制越来越严格.因此,开发高效的深度加氢脱硫催化剂成为当今的热门课题之一.在柴油馏分中,由于存在空间位阻作用,二苯并噻吩(DBT)及其烷基取代的衍生物是最难脱除的.传统的加氢脱硫(HDS)催化剂通常是将活性金属担载在γ-Al2O3上.近年来,介孔材料如MCM-41,SBA-15,HMS,KIT-1和KIT-6等也被用作加氢脱硫催化剂载体,其大的比表面积有利于活性组分分散,大的规则孔径有利于反应物和产物扩散.其中,KIT-1介孔分子筛具有三维短蠕虫状介孔结构和大的比表面积,其酸性和水热稳定性都高于MCM-41.然而,由于无定形的孔壁使得介孔分子筛的酸性和水热稳定性较差,限制了其在石油化工领域的应用.而介微孔复合分子筛兼具了微孔分子筛酸性强、水热稳定性好和介孔分子筛的孔道优势,因此一经出现就引起了研究者广泛关注.有研究认为,增加载体酸性有利于加氢及促进C-S键氢解反应.载体中的微孔可高效吸附氢分子,降低HDS过程所需的温度和压力,实现温和条件下燃油超深度脱硫.目前,已有研究者将Y-MCM-41,介孔ZSM-5及Beta-KIT-6等多级孔分子筛用作催化剂载体,并进行了加氢脱硫性能研究,取得了良好效果.我们曾利用双模板剂一步晶化法水热合成了介微孔复合分子筛ZK-1.该分子筛既具有与KIT-1相似的短蠕虫状三维介孔孔道,又具有ZSM-5的微孔结构.其介孔孔径为2.7 nm,微孔孔径为0.6nm.该分子筛具有良好的水热稳定性和较高的酸性.本文在上述研究基础上,以不同硅铝比的ZK-1为载体通过过量浸渍法担载Co,Mo活性组分制备了CoMo/ZK-1 (Si/Al=30)和CoMo/ZK-1 (Si/Al=40)催化剂,并以相同方法制备了CoMo/γ-Al2O3,CoMo/AlKIT-1,CoMo/ZSM-5和CoMo/Mix(等量的ZSM-5和AlKIT-1混合物)催化剂作为对比.催化剂的N2吸附和NH3程序升温脱附表征结果表明,CoMo/ZK-1具有高于其他催化剂的比表面积(约700 m2/g)和介微孔结构,介孔孔径和微孔孔径分别为2.3 nm和0.6-1 nm.CoMo/ZK-1的酸量大于相同硅铝比的CoMo/AlKIT-1,这是由于ZK-1的介孔孔壁上含有沸石结构单元.通过H2程序升温还原表征可知,CoMo/ZK-1的高温氢耗峰面积较CoMo/γ-Al2O3和CoMo/ZSM-5相比明显减小,表明在CoMo/ZK-1上难还原的组分数量减少,载体与金属之间的相互作用减弱,这有利于金属组分的还原和硫化.紫外-可见漫反射光谱表征结果表明,在ZSM-5表面形成了大量的聚合态氧化钼物种,这是由于载体表面积小,金属组分分散不均匀.Co2AlO4或Co2SiO4相的出现是由于载体与金属间存在较强的相互作用.以ZK-1和AlKIT-1为载体的催化剂则避免了该情况的发生.从高分辨透射电镜照片可知,MoS2在ZK-1表面分散很均匀,其堆垛层数(2.5-2.7层)和片晶长度(3.9-4.0 nm)都达到较理想的数值,有利于形成更多的Co-Mo-S(Ⅱ)活性相.以二苯并噻吩为模型化合物,采用固定床反应器考察了上述6种催化剂的加氢脱硫活性.催化剂的脱硫率从高到低依次为:CoMo/ZK-1 (40)＞ CoMo/ZK-1 (30)＞ CoMo/γ-Al2O3＞ CoMo/ZSM-5＞ CoMo/Mix＞ CoMo/AlKIT-1.在较温和的反应条件(320℃,3MPa,WHSV=5h-1)下,CoMo/ZK-1对DBT的脱硫率达到93％以上.其原因主要是:(1)ZK-1的大比表面积使Co,Mo活性组分高度分散在载体表面;(2)载体与金属之间较适中的相互作用有利于活性组分的还原与硫化;(3)ZK-1含有的沸石结构单元使其比AlKIT-1具有更多的酸中心,有利于提高HDS反应活性.     

Hydrogen and oxygen effect on homoexchange rate of ethylene over highly dispersed silver catalysts

Promoting effects of hydrogen and oxygen on the homoexchange rate of ethylene over highly dispersed silver catalysts has been established. On bulk silver no homoexchange is observed under the same conditions.

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Production of a highly dispersed carbon material and hydrogen from natural gas in a microwave reactor with metallic catalysts

Effect of a microwave field on metallic catalysts was studied in the reaction of decomposition of methane into hydrogen and highly dispersed carbon. The dependence of the conversion of methane, yield of carbon, and its composition on the chemical nature of a catalysts and reaction conditions was examined.