Carbon nanocatalysts

NP carbon nanocatalysts were obtained by impregnation of different mesoporous carbons with colloidal solutions of Ru NPs or Pd NPs previously prepared from [Ru(COD)(COT)] or [Pd2(dba)3] = 3bar THF), in the presence of PPP or triphenylphosphine and... 

Tsang, S.C., Caps, V., Paraskevas, I., Chadwick, D. and Thompsett, D. (2004) Magnetically separable, carbon-supported nanocatalysts for the manufacture of fine chemicals. Angewandte Chemie International Edition, 43 (42), 5645-5649. 

An efficient, low temperature oxidation catalyst was developed based on highly disperse metal catalyst on nanostructured Ti02 support. Addition of dopants inhibits metal sintering and prevents catalyst deactivation. The nanostructured catalyst was formulated to tolerate common poisons found in environments such as halogen- and sulfur-containing compounds. The nanocatalyst is capable of oxidizing carbon monoxide and common VOCs to carbon dioxide and water at near ambient temperatures (25-50 °C). 

A well-distributed deposition of Pt/C nanocatalyst and Nafion ionomer on bofh hydrophilic and hydrophobic carbon-based electrodes has been successfully obfained using a Pt/C concentration of 1.0 g/L, an electrical field of 300 V/cm, and a deposition time of 5 minutes [118]. The deposition of Pt/C nanocatalysts and Nafion solution via the electrophoretic process gives rise to higher deposition efficiency and a uniform distribution of catalyst and Nafion ionomer on the PEMFC electrodes. 

Louh, R. R, Huang, H., and Tsai, F. Novel deposition of Pt/C nanocatalysts and Nation solution on carbon-based electrodes via electrophoretic process for PEM fuel cells. Journal of Fuel Cell Science and Technology 2007 4 72-78. 

A variety of industrial catalytic processes employ small metal-particle catalysts on porous inorganic supports. The particle sizes are increasingly in the nanometre size range which gives rise to nanocatalysts. As described in chapter 1, commonly used supports are ceramic oxides, like alumina and silica, or carbon. Metal (or metallic) catalysts in catalytic technologies contain a high dispersion of nanoscopic metal particles on ceramic oxide or carbon supports. This is to maximize the surface area with a minimum amount of metal for catalytic reactions. It is desirable to have all of the metal exposed to reactants. 

Figure 6.7. Pd nanocatalyst on carbon for CFC conversion to HFC. In situ ETEM reaction (a) room temperature (b) atomic-scale sintering at 300 °C suggesting Ostwald ripening.

Fig. 25. (a) SEM-BSE image and (b) STEM-HAADF image of palladium nanocatalysts on a carbon support (119). 

The electrocatalytic oxidation of ethanol has been investigated for many years on different platinum-based electrodes, including Pt/X alloys (with X = Ru, Sn, Mo, etc ), and dispersed nanocatalysts. Pme platinum smooth electrodes are rapidly poisoned by some strongly adsorbed intermediates, such as carbon monoxide, resulting from the dissociative chemisorption of the molecule, as shown by the first experiments in infrared reflectance spectroscopy (EMIRS). Both kinds of adsorbed CO, either linearly-bonded or bridge-bonded to the platinum surface, are observed. Besides, oth-... 

During use, the commercial carbon-supported mercuric chloride deactivates primarily as the result of loss of mercury from the reactor [250]. This is not the case for gold catalysts since, under the reaction conditions used, no gold is lost from the catalyst. In this case, deactivation, as a result of the reduction of Au +, is readily overcome by co-feeding NO. Hence, supported gold nanocatalysts should be the catalysts of choice for this reaction. 

The three-step precursor concept for manufacture of heterogeneous egg-shdl nanocatalysts was developed in the 1990s [8-11]. The catalyst precursor is manufactured by dipping the supports into an organic or aqueous media containing the dispersed precursor at ambient temperature to adsorb the pre-prepared particles. A standard procedure for the manufacture of an egg-shell Pt 3-nm nanocatalysf via adsorption of a pre-prepared Pt hydrosol on e.g. Degussa active carbon 196 [127, 128] is ... 

The example shows that the three-step preparation procedure described above produces true nanocatalysts having naked metal particles of defined size deposited on the support surface. Generally, carbon-supported colloidal pre-catalysts are conditioned at 300 C. However, individual heating and gas flow conditions may be optimized for every catalyst system on the basis of TGA-MS analysis data. For example, the optimum temperatures for conditioning supported nanometaUic pre-catalysts having tetraoclylammonium or aluminum-organic protective shells are 280 °C and 250 G respectively [96, 126]. 

As shown by Gonzalez et al. [42], carbon supported nanocatalysts have been studied for the oxidation of methanol and other fuels. There is, however, a problem in the comparison of results, because the catalysts have been prepared by a variety of different methods. 

Mathiyarasu 1, Phani KLN (2007) Carbon-supported palladium-cobalt-noble metal (Au, Ag, Pt) nanocatalysts as methanol tolerant oxygen-reduction cathode materials in DMFCs. 

Samsung SDI has developed a prototype of DMFC for use in laptops which is quoted to have a durability almost twice as compared to other systems being developed. SAIT has reduced the amount of catalyst required by 50 %, by developing a mesoporous carbon material, which supports highly efficient 3 nm nanocatalyst particles. In addition, SAIT has developed a unique concept of nanocomposite membrane to reduce methanol crossover by more than 90 %. This composite uses a 30-100 pm thick proton-conducting membrane with a proton conductivity of 0.1 S.cm . The DMFC has an energy density of 650 Wh dm , and fed with about 200 cm of liquid methanol can supply power to a laptop for about 15 h. The cell measures 23 cm x 8.2 cm x 5.3 cm, and its weight is less than 1 kg [60]. 

One can imagine that the Pt2Ru4(CO)ig cluster compound is the intermediate in the reaction (2). The reaction can be further made via chemical decomposition of the compound to generate the bimetallic nanocatalyst. Indeed, Nuzzo et al. demonstrated that mixed Pt-Ru nanoparticles, with an extremely narrow size distribution (particle size 1.4 ran), were obtained. The Pt-Pt, Pt-Ru, and Ru-Ru coordination distances in the precursor (2.66, 2.64, and 2.84 A) changed to 2.73, 2.70, and 2.66 A, respectively, on the mixed-metal nanoparticles supported onto carbon black, with an enhanced crystalline disorder, as revealed by X-ray absorption fine stmcture (XAFS) spectroscopy. However, this example, using a controlled pyrolysis onto a designed molecirlar cluster, succeeds... 

A stable and reusable CuO/carbon nanotube catalyst (CuO/MWCNT) for N-arylation of imdazole was developed by Karvembu et al. TEM images of the nanocatalyst showed good adhesion of CuO nanoparticles to anchoring sites of acid-treated MWCNTs. Even a small amount of the catalyst (0.98 mol%) was sufficient for the coupling reactions of imidazole and aryl halides. Additionally, a variety of the desired V-arylimidazoles were smoothly generated (11 examples, at 120°C for 24 h, 44%-96% yields) (Gopiraman et al., 2013). However, the application scope of the method is limited because only electron-poor aryl halides have been investigated. 

Li X, Hsing IM (2006) Flectrooxidation of formic acid on carbon supported Pt jPdi j (x=0-l) nanocatalysts. Electrochim Acta 51 3477-3483... 

Support materials play an important role on the activity of catalysts and on lowering the amount of metals required in developing catalysts. For example, Hu et al. [22] recently reported the synthesis of S-HCNF-supported Pd nanocatalyst (Pd-S-HCNFs, Fig. 6.2) and compared its activity with Pd/C and found that both support materials gave the same onset potential but the current density at S-HCNF was about 2.3 times higher than that at the commercial carbon. 

Pd-Au [84] Plasma co-sputtering method on a carbon diffusion layer Gas diffusion layers (GDLs) 0.5 V vs. RHE Plasma sputtering method leads to more active bimetallic Pd-Au nanocatalyst than from wet chemistry method. Better (0.5 vs. 0.63 V) and current density ( 2.2 times higher)... 

Modibedi RM, Masombuka T, Mathe MK (2011) Carbon supported Pd-Sn and Pd-Ru-Sn nanocatalysts for ethanol electrooxidation in alkaline medium. Int J Hydrogen Energy 36 4664-4672... 

He Q, Chen W, Mukerjee S, Chen S, Laufek F (2009) Carbon-supported PdM (M=Au and Sn) nanocatalysts for the electrooxidation of ethanol in high pH media. J Power Sources 187 298-304... 

Ramulifho T, Ozoemena KI, Modibedi RM, Jafta CJ, Mathe MK (2013) Electrocatalytie Oxidation of Ethylene Glycol at Palladium-Bimetallic Nanocatalysts (PdSn and PdNi) Suppruted on Sulfonate functionalised Multi-walled Carbon Nanotubes. J Electroanal Chem 692 26-30... 

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