Carbon nanotubes as catalyst support

Wang X, Li WZ, Chen ZW, Waje M, Yan YS. 2006. Durability investigation of carbon nanotube as catalyst support for proton exchange membrane fuel cell. J Power Sources 158 154-159. 

Cleemann et al. [83] showed strong dependence of the fuel cell performance degradation on the catalyst supports. Graphitized carbon black and multi-walled carbon nanotubes as catalyst supports showed improvement in the catalyst and fuel cell durability. Further wrapping the carbon nanombes by a polymer, e.g., PBl [87] or pyridine-containing polybenzimidazole (PyPBl) was found to improve the utilization efficiency and durability. The... 

The aim of the present article is to report the use of carbon nanotubes as eatalyst support for a palladium active phase in the selective C=C hydrogenation of cinnamaldehyde in liquid-phase. Such reaction is of interest especially in the fine chemieal domain where speeific hydrogenation is actively sought. The catalytic performance was evaluated by comparing the observed activity and selectivity with those of a commercial catalyst supported on a high surfece area activated chareoal. The influenee of the support morphology and microstructure on the hydrogenation activity and selectivity will also be discussed. 

Carbon Nanotubes as a Support for Catalyst in Fuel Cells 271... 

The potential of carbon nanomaterials for the Fischer-Tropsch synthesis was investigated by employing three different nanomaterials as catalyst supports. Herringbone (HB) and platelet (PL) type nanofibers as well as multiwalled (MW) nanotubes were examined in terms of stability, activity, and selectivity for Fischer-Tropsch synthesis (FTS). 

Concerning the Fischer-Tropsch synthesis, carbon nanomaterials have already been successfully employed as catalyst support media on a laboratory scale. The main attention in literature has been paid so far to subjects such as the comparison of functionalization techniques,9-11 the influence of promoters on the catalytic performance,1 12 and the investigations of metal particle size effects7,8 as well as of metal-support interactions.14,15 However, research was focused on one nanomaterial type only in each of these studies. Yu et al.16 compared the performance of two different kinds of nanofibers (herringbones and platelets) in the Fischer-Tropsch synthesis. A direct comparison between nanotubes and nanofibers as catalyst support media has not yet been an issue of discussion in Fischer-Tropsch investigations. In addition, a comparison with commercially used FT catalysts has up to now not been published. 

Carbon is unique among chemical elements since it exists in different forms and microtextures transforming it into a very attractive material that is widely used in a broad range of electrochemical applications. Carbon exists in various allotropic forms due to its valency, with the most well-known being carbon black, diamond, fullerenes, graphene and carbon nanotubes. This review is divided into four sections. In the first two sections the structure, electronic and electrochemical properties of carbon are presented along with their applications. The last two sections deal with the use of carbon in polymer electrolyte fuel cells (PEFCs) as catalyst support and oxygen reduction reaction (ORR) electrocatalyst. 

Janowska, I. Hajiesmaili, S. Begin, D. Keller, V. Keller, N. Ledoux, M.-J. Pham-Huu, C., Macronized aligned carbon nanotubes for use as catalyst support and ceramic nanoporous membrane template. Catal. Today 2009,145 76-84. 

Since the synthesis of carbon nanotubes by Iijima [1, 2], a lot of investigations have been made on this kind of novel material [3-16]. Carbon nanotubes can be conventionally synthesized with several methods [17, 18], Recently, catalytic synthesis method has been developed to prepare carbon nanotubes on Co/Si02 [19, 20]. Hemadi et al. first extended the catalytic synthesis to the use of zeolites (NaY, HY and ZSM-5) as catalyst supports to synthesize carbon nanotubes [21]. 

It is well known that catalyst support plays an important role in the performance of the catalyst and the catalyst layer. The use of high surface area carbon materials, such as activated carbon, carbon nanofibres, and carbon nanotubes, as new electrode materials has received significant attention from fuel cell researchers. In particular, single-walled carbon nanotubes (SWCNTs) have unique electrical and electronic properties, wide electrochemical stability windows, and high surface areas. Using SWCNTs as support materials is expected to improve catalyst layer conductivity and charge transfer at the electrode surface for fuel cell oxidation and reduction reactions. Furthermore, these carbon nanotubes (CNTs) could also enhance electrocatalytic properties and reduce the necessary amount of precious metal catalysts, such as platinum. 

Li, W. et al.. Carbon nanotubes as support for cathode catalyst of a direct methanol fuel cell. Carbon, 40, 791, 2002. 

At the beginning of the 2U century, it is thought that the improvement of the existing chemical industry will pass through the development of new kinds of catalysts to meet the latest environmental requirements. Since their discovery in 1991 [1], carbon nanotubes and nanofibers have received increasing interest in academic research and for several potential applications [2-4]. It has been reported by different authors that carbon nanofibers could be efficiently used as catalyst support for several catalytic reactions either in gas or in liquid phase [5-7], In both cases, the carbon nanofiber based catalysts always exhibited higher catalytic performances compared to those observed on equivalent conventional catalysts. 

The aim of the present article is to report the large scale (several hundred grams per gram of active phase) synthesis of uniform carbon nanofibers (average diameter ranging between 40 and 60 nm) by the catalytic decomposition of a mixture of ethane and hydrogen over a nickel catalyst supported on carbon nanotubes. To illustrate their catalytic potential, the as-synthesized carbon nanofibers are subsequently used as catalyst support for palladium in the hydrogenation of nitrobenzene in a liquid phase reaction. 

Since their discovery in 1991 [1], carbon nanotubes have received great attention due to their unique chemical and physical properties which render them attractive in several potential applications [2]. Among them, the use of nanostructured carbon as catalyst support seems to be very promising according to the last results reported in the literature [3-5]. 

Chun YS, Shin JY, Lee SC et al (2008) Palladium nanoparticles supported onto ionic carbon nanotubes as robust recyclable catalysts in an ionic liquid. Chem Commun 8 942-944... 

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... 

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. 

A crucial problem connected to carbon nanotube synthesis on supported catalysts on an industrial scale is the purification step required to remove the support and possibly the catalyst from the final material. To avoid this costly operation, the use of CNT- or CNF-supported catalysts to produce CNTs or CNFs has been investigated. Although most catalytic systems are based on nickel supported on CNFs (see Table 9.4), the use of MWCNTs [305,306] or SWCNTs [307] as supports has also been reported. Nickel, iron [304,308-310], and bimetallic Fe-Mo [305] and Ni-Pd [295] catalysts have been used. Compared to the starting CNTs or CNFs, the hybrid materials produced present higher specific surface area [297,308] or improved field emission characteristics [309]. 

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. 

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