Preparation and catalytic efficiency of mixed noble metal catalysts on electrochemically activated carbon fibre supports

Mixed noble metal catalytic systems were prepared on electrochemically activated PAN-based carbon fibre supports through a procedure of repetitive cation exchange between the acidic (-OOOH and-OH) groups of the electrooxidized carbon surface and noble metal salts and subsequent cathodic reduction of the exchanged noble metal ions to the metallic state.The whole investigation was carried out for the binary system Ag-Pd. The catalytic efficiency of palladium deposited on silver is more pronounced compared to a Pd-deposition obtained after only one Pd²⁺-exchange procedure and subsequent cathodic reduction, whereas an inhibition of the catalytic activity of palladium is noticed when it is covered by silver deposition. The catalytic efficiency of the obtained mixed noble metal catalysts was studied by means of hydrogen-adsorption and absorption profiles in H₂SO₄, the electroreduction of nitrobenzene in aqueous methanolic H₂SO₄ solutions and the hydrogenation reaction of nitrobenzene to aniline in methanolic solutions. The study was completed by impedance spectroscopic measurements at the potential of hydrogen evolution in H₂SO₄ solutions.Mixed Ag-Pd systems are even more stable than double Pd-Pd depositions on activated carbon fibre supports, as shown by the fact that they retain their mechanical stability and catalytic activity even after prolonged storage in aqueous or methanolic solutions, as well as after ultrasonic treatment.     

活性炭纤维在催化领域中的应用

介绍了活性炭纤维(ACF)的表面化学结构、催化特性及其在催化中的研究与应用:脱硫反应,除 NO的反应,电极法处理废水;综述了ACF的载体功能:负载金属、金属氧化物、金属氢氧化物、杂多酸等催化 剂。指出需进一步研究氮含量在脱硫过程中所起的作用,以及作为ACF催化氧化活性位的官能团种类。进 一步研究负载物与载体间存在的相互作用,进而获得性能良好的ACF负载型催化剂。     

Synthesis of carbon nanotubes grown by hot filament plasma-enhanced chemical vapor deposition method

We prepared two kinds of catalytic layers onto n-typed silicon substrate—nickel by r.f.-magnetron sputtering and iron (III) nitrate metal oxide by spin coating. For iron (III) nitrate metal oxide 0.5 mol of ferric nitrate nonahydrate [Fe₂(NO₃)₃·9H₂O] ethanol solution was coated onto silicon by spin coater at different rotation speeds (rev./min). Carbon nanotubes were synthesized on both Ni and iron (III) nitrate metal oxide layers by the HFPECVD (hot filament plasma-enhanced chemical vapor deposition) method. We used ammonia (NH₃) and acetylene (C₂H₂) for the dilution gas and a carbon precursor for the growth of the carbon nanotubes, respectively. We could observe the relationship between the catalytic cluster density and the nanotube density with scanning electron microscopy (SEM) images. The density of carbon nanotubes on iron (III) nitrate metal oxide was controlled by the rev./min of the spin coater. Transmission electron microscopy (TEM) image shows multi-walled carbon nanotube where the catalyst was found in the tip of the carbon nanotube. Electron dispersive X-ray spectrometry (EDS) peaks for CNT's tip show that it was constituted with nickel and iron, respectively. Raman spectroscopy of nanotubes shows D-band and G-band peaks approximately 1370 and 1590 cm⁻¹.     

Fe2O3/AC催化剂上对甲基苯硫酚的水相催化氧化偶联

以对甲基苯硫酚为模型底物，空气为氧化剂，来研究硫醇水相催化氧化偶联制备二硫醚。以活性炭为载体，采用等体积浸渍法制备了一系列负载型氧化物催化剂，并考察了其在对甲基苯硫酚氧化偶联制备对甲苯二硫醚反应中的催化性能。反应结果表明，活性炭负载的铁氧化物具有最佳催化性能。采用N₂物理吸附、X射线衍射、X射线光电子能谱和透射电镜等表征手段对活性炭负载的铁氧化物催化剂进行了表征。表征结果表明，铁氧化物为高度分散在活性炭上的Fe₂O₃物种。以Fe₂O₃/AC为催化剂，当催化剂焙烧温度为400℃，Fe负载量为5%，在50℃下反应30min时，对甲苯二硫醚的收率高达97.4%；该催化剂循环使用5次后活性无明显下降。     

Ordered Mesoporous Silica (OMS) Supported Vanadium Nitride and Carbide Catalysts

Nanostructured vanadium nitride and carbide catalysts were prepared by the nitridation and carburization of vanadium oxide supported on M41S materials (MCM-41 and SBA-15) and activated carbon. The oxide precursors, V₂O₅/M41S, were obtained in three different synthesis strategies using “in situ” and “ex situ” incorporation of vanadia precursors (V(acac)₃) into the mesoporous host. For the oxide precursors specific surface areas exceeding 1,200 m² g⁻¹ were achieved. After nitridation a slight decrease of surface area was observed. All VN catalysts show a high activity in propane dehydrogenation with a selectivity exceeding 80% towards propene. Impregnation and nitridation conditions have profound influence upon the catalytic activity. The highest activity was observed for VN supported on NORIT A.     

Hydroformylation of mixed octenes catalyzed by supported rhodium-based catalyst

In order to solve the difficult separation between catalyst and products in homogeneous system, the activated carbon (AC)-supported rhodium-based catalyst (Rh/AC) was prepared. Hydroformylation of mixed octenes catalyzed by Rh/AC was studied, and compared to that catalyzed by RhCl(CO)(TPPTS)₂ [TPPTS: trisodium salt of tris(m-sulphonylphenyl) phosphine], and [Rh(CH₃COO)₂]₂-Ph₃PO (Ph₃PO: triphenyl phosphine oxide). The performance test of the catalysts showed the Rh/AC presented higher catalytic activity, selectivity and air-stability. During the recycle experiments Rh/AC could be used 4 times without significant loss of rhodium. The effects of the supports, rhodium loading and reaction conditions on the catalytic performance of Rh/AC were investigated. The results showed petroleum coke-based activated carbon with higher surface area and more basic groups was advantageous to the formation of aldehydes. The heterogeneous Rh/AC catalyst displayed higher catalytic activity and reusability.     

Effect of Hydrogen Treatment on the Catalytic Activity of Iron Oxide Based Materials Dispersed Over Activated Carbon: Investigations Toward Hydrogen Peroxide Decomposition

The effect of hydrogen treatment (400 °C/1 h) on the catalytic properties toward H₂O₂ decomposition of iron oxide based materials dispersed over activated carbon were investigated. Two different supports were evaluated: a commercial activated carbon (ACM) and an activated carbon produced from spent coffee grounds (ACR). The catalysts were characterized using XRD, SEM, N₂-sorption, XPS and TPR analysis. The main results suggest the formation of composites with high surface area (>800 m² g^?1) and the hydrogen treatment resulted in a great increase in the catalytic activity, probably as a function of the reduced iron species (Fe²⁺ and Fe⁰) formed with the treatment. Moreover, the catalyst prepared with ACR showed to be more active than that prepared from ACM.     

Dual role of activated carbon as fuel and template for solution combustion synthesis of porous zinc oxide powders

In this work, nanosized zinc oxide (ZnO) powders were fabricated by urea–nitrate solution combustion synthesis using activated carbon as a structure-directing template and secondary fuel at different fuel–oxidant ratios. The as-synthesized powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption–desorption measurements, UV–Vis diffuse reflectance spectroscopy, and photoluminescence. The effect of fuel amount on photocatalytic activity of ZnO powders was evaluated by the degradation of an azo dye Orange G. It was observed that combustion synthesis with activated carbon as a secondary fuel had a profound effect on reducing crystallite size and enhancement of specific surface area. The crystallite size of the as-synthesized powders varied from 46 to 26 nm. The ZnO powder prepared at a fuel–oxidant ratio of 1.8 possessed the small crystallite size and high specific surface area of 69 m²/g. It correspondingly resulted in the highest dye removal percentage of 99% with a rate constant of 0.027 min⁻¹. The improvement in dye degradation can be due to the synergistic interaction and interplay of enhanced surface area and catalytic ability of the photocatalyst. This study provides a simple single-step synthesis methodology to produce metal oxide nanopowders with tunable surface properties for high potential applications in catalysis, optoelectronics, and gas sensors.     

Selective Reduction of NO with CO Over Titania Supported Transition Metal Oxide Catalysts

A series of transition metal oxides promoted titania catalysts (MO _x /TiO₂; M = Cr, Mn, Fe, Ni, Cu) were prepared by wet impregnation method using dilute solutions of metal nitrate precursors. The catalytic activity of these materials was evaluated for the selective catalytic reduction (SCR) of NO with CO as reductant in the presence of excess oxygen (2 vol.%). Among various promoted oxides, the MnO _x /TiO₂ system showed very promising catalytic activity for NO + CO reaction, giving higher than 90% NO conversion over a wide temperature window and at high space velocity (GHSV) of 50,000 h⁻¹. It is remarkable to note that the catalytic activity increased with oxygen, up to 4 vol.%, under these conditions leading primarily to nitrogen. Our TPR studies revealed the presence of mixed oxidation states of manganese on the catalyst surface. Characterization results indicated that the surface manganese oxide phase and the redox properties of the catalyst play an important role in final catalytic activity.     

Effect of heat treatment of activated carbon supports on the loading and activity of Pt catalyst

The study has been done on the effect of heat treatment of activated carbon at 1573-1773 K on its structural and electronic properties as a catalyst support. The X-ray diffraction result indicated that a partly graphitized structure was formed when the activated carbon was heated to a high temperature (1673 K). From the X-ray photoelectron spectroscopy result, it was found that Pt⁰ concentration was increased, but PtO and PtO₂ concentrations were decreased with an increase in the heat treatment temperature. From the van Dam’s model applied to this result, it might be concluded that more “π-sites” are created as the heat treatment temperature becomes higher. From the CO-chemisorption result, the highest loading was observed in case of Pt/AC1673 sample. This improved loading ability could be explained by the special interaction of the graphitic planes (π-sites) with the metal particles. Based on the catalytic activity, CO-chemisorption and XPS results, it is concluded that the well-loaded Pt⁰ species mainly contribute to the catalytic activity. Moreover, it was found that different degrees of graphitization of heat treated activated carbon could cause different surface Pt⁰ and improve the resistance of carbon support against gasification under air oxidation.     

Partial oxidation of ethane to syngas over nickel‐based catalysts modified by alkali metal oxide and rare earth metal oxide

The catalytic activity, thermal stability and carbon deposition of various modified NiO/γ‐Al₂O₃ and unmodified NiO/γ‐Al₂O₃ catalysts were investigated with a flow reactor, XRD, TG and UVRRS analysis. The activity and selectivity of the NiO/γ‐Al₂O₃ catalyst showed little difference from those of the modified nickel‐based catalysts. However, modification with alkali metal oxide (Li, Na, K) and rare earth metal oxide (La, Ce, Y, Sm) can improve the thermal stability of the NiO/γ‐Al₂O₃ and enhance its ability to suppress carbon deposition during the partial oxidation of ethane (POE). The carbon deposition contains graphite‐like species that were detected by UVRRS. The nickel‐based catalysts modified by alkali metal oxide and rare earth metal oxide have excellent catalytic activities (C₂H₆ conversion of ~100%, CO selectivity of ~94%, 7 × 10⁴ l/(kg h), 1123 K), good thermal stability and carbon‐deposition resistance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Copolymerization of carbon dioxide and epoxides with a novel effective Zn–Ni double‐metal cyanide complex

A novel double‐metal cyanide complex based on Zn[Ni(CN)₄] was prepared and used as a catalyst for the copolymerizations of carbon dioxide and propylene oxide (PO) and carbon dioxide and cyclohexene oxide (CHO). The copolymers were characterized by IR and ¹H‐NMR, and the effects of temperature, pressure, solvent, and preparative methods for the catalysts on catalytic activity and composition of the copolymer were investigated. The results show that this novel catalyst exhibited its highest catalytic efficiency at about 500 g/g of Zn[Ni(CN)₄] for PO and CO₂, whereas the catalytic efficiency for CHO and CO₂ was merely between 5.6 and 22.5 g/g of Zn[Ni(CN)₄]. The molar fraction of carbonate linkages for PO–CO₂ and CHO–CO₂ copolymers reached about 0.6 and 0.3, respectively. The results show that a lower temperature and a higher CO₂ pressure were favorable for the incorporation of CO₂ into the copolymer, and the nonpolar solvents were better media for copolymerization. As a complexing agent, glycol ether exhibited better promoting effects on catalytic efficiency among those investigated, but the catalysts prepared by different complexing agents showed no significant differences in the compositions of the copolymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nickel Nanoparticles Dispersion on Carbon Molecular Sieve by Electroless Deposition

This work presents a novel one step process to synthesize nickel nanoparticles dispersed on activated carbon. This technique is widely used for the plating of metal surfaces and consists of the immersion of substrate on a stabilized bath that contains the metal precursor, a complexing agent, an additive for pH control, and chemical stabilizer to avoid the spontaneous reduction of metal in bath solution. By this process, nickel was dispersed on chemical activated carbon (carbon molecular sieve, CMS) obtaining a catalyst which showed better catalytic activity on benzene dehydrogenation than the observed for unsupported nickel nanoparticles and a commercial catalyst composed by nickel nanoparticles supported in Al₂O₃?CSiO₂.     

Catalytic activity of tungstophosphoric acid supported on carriers of diverse acidity in the synthesis of enaminones

Tungstophosphoric acid (PW), supported on different metal oxide (TiO₂, γ-Al₂O₃, K 10 and KSF) and activated carbon were used in the condensation of aniline with ethylacetoacetate to afford the corresponding β-enaminone. Catalytic activity was discussed in relation with the acid strength of catalysts. The best catalytic activity was obtained with PW/TiO₂. Effect of PW loading, solvent and catalyst reusability was studied to introduce the best reaction conditions. Based on the above experimental findings, various β-enaminones were synthesized in excellent yield within a few minutes under solvent free condition.     

A flexible carbon counter electrode for dye-sensitized solar cells

A pure carbon counter electrode (CE) for dye-sensitized solar cells (DSCs), has been fabricated using an industrial flexible graphite sheet as substrate and activated carbon as the catalytic material. The CE shows very low series resistance (Rs) and charge-transfer resistance (Rct) by combining the high conductivity of the flexible graphite with the high catalytic property of activated carbon. The Rs and Rct for the CE are respectively only a quarter and two-thirds of those for a platinized fluorine-doped tin oxide glass (Pt/FTO). DSCs with cell areas of 0.15 and 1 cm² fabricated with this CE show higher solar-to-electricity conversion efficiencies. The respective values are 6.46% and 5%, compared with 6.37% and 2.91% for the Pt/FTO based devices.     

Carbon materials as catalyst supports for SO2 oxidation: catalytic activity of CuO-AC

Copper catalysts supported on acid treated activated carbon (AC) were prepared, characterized and tested in terms of their SO₂ oxidation activity. Reactions of CuO-AC in flow systems with sulfur dioxide, oxygen and nitrogen streams were investigated to determine the types of chemical interactions that occur on the sorbent surface. The effects of reaction temperature, acid treatment, metal loading, support particle size, SO₂ concentration and O₂ concentration on SO₂ oxidation activity were evaluated. It was found that carbon materials used as catalyst supports for copper oxide catalysts provided a high catalytic activity for adsorbing SO₂ from flue gas and oxidizing it. Acid pretreatment of the carbon supports increased the content of specific surface chemical groups to enhance the catalytic activity for SO₂ oxidation. Metal loading, as well as support particle size, have a significant influence on the SO₂ activity. The supported metals rather than surface oxygen functional groups on AC may be the active sites for adsorbing SO₂.     

Comparative energy barriers for hydrogen activation by homogeneous and heterogeneous metal oxide catalysts

Triethylene glycol solutions of alkali and alkaline earth metal hydroxide complexes are well-defined soluble oxide water-gas shift catalysts which equilibrate the reaction of carbon monoxide and water to yield hydrogen and carbon dioxide at temperatures ranging from 150 ° to 250 °C and carbon monoxide pressures of 1 to 300 atm. Significantly, catalysis proceeds cleanly, even in the complete absence of a metal center in the soluble oxide system. Thus, the rate of hydroxide ion catalyzed hydrogen evolution is highest in the presence of a noncoordinating organic cation: Bu_ΔN⁺>Cs⁺>Na⁺>H⁺>Ca⁺². Furthermore, the activation energy for the homogeneous sodium hydroxide catalyst in triethylene glycol solution, 26±1 kcal, is comparable to that exhibited by a commercially used heterogeneous iron oxide catalyst, 27±0.2 kcal. The alkali metal hydroxide system may be modified for metal cocatalysis. Thus, lead (II) oxide dissolves in the triethylene glycol solutions to yield a new species which exhibits a²⁰⁷Pb NMR resonance shifted 3350 ppm downfield from lead perchlorate. The activity of this lead modified system is improved by three orders of magnitude. Yet, the activation energy is unchanged, 26±1 kcal, suggesting that entropic factors may be important in these homogeneous metal oxide hydrogen evolution/activation systems.     

Suzuki Coupling Reactions in Pure Water Catalyzed by Supported Palladium – Relevance of the Surface Polarity of the Support

Heterogeneous (supported) palladium catalysts like palladium on carbon and a variety of metal oxides have been shown to be highly active for Suzuki coupling reactions in neat water under mild reaction conditions (T=65 °C). It has been demonstrated for the first time that hydrophobic effects of the catalyst surface play an important role for the catalyst activity in water. Catalysts possessing hydrophobic surfaces (e.g., palladium on carbon) show higher activity for Suzuki coupling reactions in water than their hydrophilic counterparts (palladium on metal oxides). Tuning of the surface polarity of metal oxide supports (by silylation) results in higher activity under these conditions. Stronger alkaline conditions (three‐fold excess of base) compensate the effect of hydrophobic supports and result in high activity of the catalysts also with hydrophilic supports. The addition of tetrabutylammonium bromide to generate, activate and stabilize the catalytic species (dissolved palladium complexes) is necessary for the conversion of more demanding substrates. The reaction is considered to be homogeneous taking place near the catalyst surface inside a droplet or layer of the reactant.     

活性炭负载金属氧化物常温脱除低浓度NO

在活性炭上负载了金属氧化物用于低浓度NO在常温下的脱除。活性炭在使用之前经过了氧化预处理,经过硝酸氧化处理后,活性炭表面的羰基和硝基数量均增加,对NO的脱除能力显著提高。在硝酸处理后的活性炭上负载了金属氧化物,其中Ce和Co负载的样品对NO的脱除效果最佳,与未负载的样品相比脱除量提高了约8倍。进一步研究发现被脱除的NO最终以金属硝酸盐的形式存在,说明NO在通过催化氧化吸附剂层时首先被氧化生成NO2,之后NO2与负载的金属氧化物反应生成了金属硝酸盐。     

Effect of promoters on catalytic performance of Cr/SiO2 catalysts in oxidative dehydrogenation of ethane with carbon dioxide

Several acidic and basic oxide promoted Cr/SiO₂ catalysts were prepared and investigated in oxidative dehydrogenation of ethane in the presence of carbon dioxide. The effects of SO₄ ^2–, WO₃ and alkali metal oxides (Li₂O, Na₂O, and K₂O) on the catalytic activity were studied. It is found that sulfation of silica produces a positive effect on ethane conversion and ethylene yield while tungstation and addition of strong basic promoters (alkali metal oxides) suppress the catalytic activity. Characterization indicates that the varying activity of the promoted catalysts can be attributed to the difference in acid/base property and redox potential.