Carbon nanotubes catalytic process applications

It occurs catalytically on the surface of Fe nanoparticles grown from Fe(CO)5. Also, the conventional synthesis of nanotubes by catalytic CVD from acetylene or methane can be formally considered as redox reaction. Nevertheless, the electrochemical model of carbonization (Sections 4.1.1 and 4.1.2) is hardly applicable for CVD and HiPco, since the nanotubes grow on the catalyst particle by apposition from the gas phase, and not from the barrier film (Figure 4.1). The yield and quality of electrochemically made nanotubes are usually not competitive to those of catalytic processes in carbon arc, laser ablation, CVD and HiPco. However, this methodology demonstrated that nanotubes (and also fullerenes and onions (Section 4.3)) can be prepared by soft chemistry" at room or sub-room temperatures [4,5,101]. Secondly, some electrochemical syntheses of nanotubes do not require a catalyst [4,5,95-98,100,101]. This might be attractive if high-purity, metal-free tubes are required. 

Most processes in the fine chemical industry are typically carried out in batch mode, where the powdered catalyst is suspended in the reaction medium. For the production of bulk chemicals extruded or granulated carbon-supported catalysts are used in fixed-bed reactors. To date, the most important carbon supports from an industrial point of view is activated carbon and carbon black. The main reason for the success of those materials is their commercial availability and variety of different grades, so that the final calalyst can be lailored to the end user s requirements. On a worldwide basis, 908,000 metric tons of activated carbon was produced in 2005 [5], Only a small fraction of that is used as catalyst support. Other carbon supports, such as carbon aerogels and carbon nanotubes, are in the focus of modem catalytic research but so far have not been used in commercial processes. Since there are various scientific pubhcations in the field of carbon and its use as catalyst support, the focus of this contribution is on the industrial importance of carbon supports for precious metal powder catalysts, their requirements, properties, manufacturing, and industrial applications. 

To date, carbon materials play a major role in nanosciences (fullerenes, nanotubes), electronic industry (diamond), metallurgy (graphitic carbon), electrochemistry, catalysis, adsorption, etc, The majority of these applications have arisen because of the existence of a superficial layer of chemically bonded elements. Thus, the surface functional groups determine the self-organization, the chemical stability and the reactivity in adsorptive and catalytic processes. 

Among the studied adsorption processes which have focused on CNFs, hydrogen adsorption is the most studied one, theoretical calculations, experimental measurements and molecular simulations being reported in the literature [93]. However, only a limited number of works have focused on adsorption of organic molecules on CNFs, in spite of the potential application (adsorption filters, key step for catalytic applications, etc.). In this way, the adsorption of several organic molecules over CNFs was compared to carbon nanotubes and high surface area graphites, all of them... 

Catalyst support due to their ability to be tailored to specific needs, carbon nanotubes are candidate supports in heterogeneous catalytic processes. Carbon nanotubes are also employed as catalytic support due to their high surface area, chemical and thermal stability (in a non oxidative enviromnents). Carbon nanofibres, soot and graphite are used in these applications. 

Direct Methanol Fuel Cell (DMFC) is very attractive as energy source for portables, mobiles and stationary applications. PtRu/C electrocatalyst has been considered the best electrocatalyst and the catalytic activities depend on the preparation method [1]. Studies have been shown that the use of carbon nanotubes and mesoporous carbon as support increase the performance of the PtRu/C eleetrocatalysts, however, the synthesis of these supports are normally complex or involve harsh conditions. Recently, the synthesis of metal/carbon nanoarchitectures by a one-step and mild hydrothermal carbonization process was reported using starch or glucose and metals salts [2]. We have studied the synthesis of PtRu/C eleetrocatalysts by hydrothermal carbonization and focused especially on the effects of different carbon somces on the electrocatalytic performance for methanol oxidation. 

Porous carbons constitnte a fascinating kind of material. Different types with distinctive physical forms and properties (i.e., activated carbons, high-surface-area graphites, carbon blacks, activated carbon cloths and fibers, nanofibers, nanotubes, etc.) find a wide range of indnstrial applications in adsorption and catalysis processes. The main properties of these materials that make them very useful as catalyst supports, as well as some of their applications, have been described. The use of carbon as a catalyst support relies primarily on the relative inertness of its surface, which facilitates the interaction between active phases or between active phases and promoters, thus enhancing the catalytic behavior. This makes porous carbons an excellent choice as catalyst support in a great number of reactions. 

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