Catalysts active carbon fiber

Figure 9.2 Fiber and foam structures, (a) Knitted silica fibers catalyst. (Reprinted from [7].) (b) Woven active carbon fiber catalyst. (Reprinted from [8].) (c) Aluminum foam. (Reprinted from [9].)...

As alternative materials to traditional particulate active carbons, much research has been carried out on the potential of active carbon fibers as gas and liquid phase adsorbents and catalysts/catalyst supports, as outlined below. 

Aumo, J., Oksanen, S., Mikkola, J. P., Salmi, T. and Murzin, D. Yu., Novel Woven Active Carbon Fiber Catalyst in the Hydrogenation of Citral, Cat Today 102-103 (2005), 128-132... 

Usually the activated carbon granules are employed for chromium removal or for catalysts preparation. However in some previous reports the perspectives and advantages of activated carbon fibers (ACF) utilization for the same employment have been documented [2,4]. It seems from the analysis of the articles that the use of ACF or activated carbon cloth has a great potential. 

The use of gas diffusion electrodes is another way to achieve high current densities. Such electrodes are used in the fuel-cell field and are typically made with porous materials. The electrocatalyst particles are highly dispersed inside the porous carbon electrode, and the reaction takes place at the gas/liquid/solid three-phase boundary. COj reduction proceeds on the catalyst particles and the gas produced returns to the gas compartment. We have used activated carbon fibers (ACF) as supports for metal catalysts, as they possess high porosity and additionally provide extremely narrow (several nm) slit-shaped pores, in which nano-space" effects can occur. In the present work, encouraging results have been obtained with these types of electrodes. Based on the nanospace effects, electroreduction under high pressure-like conditions is expected. In the present work, we have used two types of gas diffusion electrodes. In one case, we have used metal oxide-supported Cu electrocatalysts, while in the other case, we have used activated carbon (ACF)-supported Fe and Ni electrocatalysts. In both cases, high current densities were obtained. 

To investigate the effect of micropores, we conducted electrolyses using the following catalysts, unmodified ACF, iron and nickel catalysts supported on non-activated carhon fibers (CF/Fe, CF/Ni), iron catalyst supported on activated carhon fibers (ACF/Fe) and two types of nickel catalysts supported on activated carbon fibers (ACF/Ni-1, ACF/Ni-2). Table 1 shows the reduction product distributions for the various catalysts at -1.8V vs. SCE. The ACF catalyst itself has very fittle activity for CO2 reduction, and hydrogen evolution was the principal reaction. The CF/Fe and CF/Ni catalysts showed very little activity as well. 

Tryk el al. studied GDEs composed of active carbon fiber and loaded with catalysts Ni, Fe, Pd metals, porphyrins, and phthalo-cyanines. The GDEs gave partial current density of CO2 reduction up to 80 mA cm 2 with production of CO under atmospheric pressure. They presumed that the nanopores present in active carbon fiber may provide quasi high pressure atmosphere due to nanoscale effect." Thus Ni electrocatalyst, which is practically inert for CO2 reduction under atmospheric pressure, may be activated in a similar manner as observed with Ni electrode under elevated pressure. " ... 

A large variety of carbon materials can and have been used as catalyst supports. The most important are granular and powdered activated carbons and carbon blacks, but there is increasing interest in related materials, such as activated carbon fibers and cloths, nanotubes, and nanofibers [8]. A comprehensive review... 

Jin et al. [52] have deposited 5 wt% Pd on activated carbon fibers by alkaline hydrolysis of palladium chloride and obtained metal dispersions of 55 to 77%. Dispersions of 40 to 50% have been reported by Farkas et al. [53], who prepared Pd/C by fast addition of NaOH solution to a suspension of carbon in an aqueous solution of K2PdCl4. More highly loaded Pd and Pt catalysts (10 wt%) have been prepared by dropwise addition of the metal salt solution to the suspension of carbon in Na2C03 solution. In this case [54], a Pt particle size of 10 nm and a Pd particle size of 17 nm were reported. Ion adsorption led to much lower particle sizes. By quick addition of NaOH solution to a suspension of carbon support in PdCl2 solntion, Cabiac et al. [55] obtained 5- to 10-nm Pd particles at a loading of about 4 wt%. Clearly, details of support, metal loading, and the method of mixing of reactants all play a vital role in the dispersion and distribution of the metal in the finished catalyst. 

Similar conclusions concerning the textural requirements of the catalyst were reached by Kane et al. [58], who attributed the differences observed with a range of CMS to the effects of the pore structures on the coupled reaction and diffusion phenomena. They suggested that the pore structure should include substantial amounts of transport pores (meso- and macropores). Pereira et al. [59] used activated carbon fibers obtained from different precursors as catalysts in the ODE. They observed that fibers with an average micropore width lower than... 

The oxidation mechanism of methanethiol on activated carbon fibers (ACF) in the presence of H2S and iron catalyst was proposed by Katoh and coworkers [78]. According to them the process is initiated by, which, through chain reactions with an iron catalyst involved, form OH radicals. Those radicals not only extract hydrogen from polysufide, form chain sulfur radicals, which accelerate the H2S oxidation but also oxidize DMDS formed by partial oxidation. As a product, methane sulfonic acid is expected. This mechanism is true only for the complex system with a mixed supply of the sulfur containing gases,... 

Hung, C. M. Activity of Cu-activated carbon fiber catalyst in wet oxidation of ammonia solution. J. Hazardous Mater. 2009,166(2), 1314-1320. 

A similar catalyst was developed by Virtanen et al. [63, 64] for the liquid-phase hydrogenation of a,P unsaturated aldehydes. The authors immobilized IL containing Pd nanoparticles on active carbon fibers. The system can be characterized as a gas-hquid-liquid-soUd system, where gaseous hydrogen and an unsaturated... 

Thermal Insulation is by far the most Important present application of oxide fibers. Transition alumina fibers, e.g., eta-alumina fibers, are produced at Intermediate firing temperatures and are used as supports for catalysts and Insulation tiles such as those used for the space shuttle orbiter [1-2]. Carbon fiber felts are used as internal thermal insulation for vacuum furnaces at extremely high temperatures. Activated carbon fibers, which are obtained by partial oxidation of selected carbon fibers, have extremely small pores and very high specific surface areas, ranging from 500 to 3000 mVg. They are of great interest in ultrafiltration as membranes for the treatment of used waters and liquids [3-5]. 

Rebouillat el al [4] and Suzuki [5] give good reviews of activated carbon fibers. Traditionally, activated carbon granules are made by the carbonization of a product such as coconut shells, which due to their physical granular form, tend to be difficult to handle and the development of an activated woven cloth by the British Chemical Defence Establishment at Porton Down [6,7] via the controlled heat treatment of a woven rayon cloth offers many advantages. The activated charcoal cloth (ACC) product was made under licence in 1977, by Charcoal Cloth Ltd. One such process used a 1.8 m wide fabric, reducing to about 1.0 m at the end of the process. To aid carbonization, the cloth was treated with a solution of chemicals to confer a measure of flame retardancy. As explained in Chapter 6, there are two forms of flame retardant—one where the flame retardant acts as a catalyst and promotes removal of the —OH groups and the other form, which actually reacts with the —OH... 

Westwood et al. prepared SCR catalyst for NO reduction by impregnating a surface oxidized activated carbon fiber from aqneons solutions of ferric nitrate, nickel nitrate, or copper nitrate followed by calcinations at 300°C under nitrogen for 2 hr. The catalytic activity of these metal loaded ACFs was determined in a plug-flow microreactor using line FT IR analysis of the feed and flue gases containing 800 ppm... 

The addition of an iron catalyst to the treated solution allows the formation of OH via Fenton s reaction (1). In 1986, M. Sudoh et al. were the first to apply the method to wastewater treatment. Since then, graphite, carbon-PTFE O2 diffusion, carbon felt, activated carbon fiber (ACF), reticulated vitreous carbon (RVC), carbon sponge, and carbon nanotubes (CNTs) have been used as cathode materials [1]. 

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