Carbon-supported metal catalysts

The most spectacular results, in terms of comparison between CFPs- and carbon-supported metal catalysts, were likely provided by Toshima and co-workers [33,34]. As illustrated in Section 3.3.3, they were able to produce platinum and rhodium catalysts by the covalent immobilization of pre-formed, stabilized metal nanoclusters into an amine functionalized acrylamide gel (Scheme 5). To this purpose, the metal nanopartides were stabilized by a linear co-polymer of MMA and VPYR. The reaction between its ester functions and the amine groups of the gel produced the covalent link between the support and the... 

Figure 13.27 illustrates a schematic view of a carbon-supported metallic catalyst in the superheated liquid-film state. 

Hodoshima, S., H. Nakamura, A. Shono, K. Satoh, and Y. Saito, Hydrogen supply from organic chemical hydride with carbon-supported metallic catalyst under superheated liquid-film conditions.. Hydrogen Energy Syst. Soc. Jpn., 30(1), 36-41 (2005). 

FUJIMOTO ET AL. Catalytic Features of Carbon-Supported Metal Catalysts 209... 

As for hydrogenation, heterogeneous catalytic oxidation of carbohydrates was essentially performed in the presence of carbon-supported metal catalysts, namely Pt, Pd or Bi-doped Pd.[57] Oxidation of glucose into gluconic acid, the worldwide production of which is around 60000 tons year 1,[52] is used in the food and pharmaceutical industry, and is produced today by enzymatic oxidation of D-glucose with a selectivity in gluconic acid close to 100%. 

The rotational spectmm of undissociated dihydrogen molecules may be observed by INS on sulfide catalysts as on carbon-supported metal catalysts. On M0S2 a peak near 120 cm , assigned to the y(l<—0) transition of the adsorbed dihydrogen molecule, was observed at... 

P.C.H. Mitchell, A.J. Ramirez-Cuesta, S.F. Parker, J. Tomkinson D. Thompsett (2003). J. Phys. Chem. B, 107, 6838-6845. Hydrogen spillover on carbon-supported metal catalysts studied by inelastic neutron scattering. Surface vibrational states and hydrogen riding modes. 

The largest exchange current density, j0, of the reaction has to be selected, if possible, since economic limitations are always prevalent in scaled-up engineering. However, with the development of nanodispersed substrates and carbon-supported metal catalysts, this limitation becomes a secondary consideration. At this point, it is important to say that most of the reported values of j usually refer to simple reactions on pure metal substrates using different shapes of electrode designs in a certain and single electrolyte. Thus, the measurement of the real j0 value at select industrial conditions of the electrochemical reactor has to be performed that is, experimental measurements cannot be avoided [4,5]. 

As discussed above, oxygen groups play a crucial role in determining the metal loading and dispersion of carbon-supported metal catalysts. Also, the pore structure is claimed to have an influence on the metal dispersion. We give a short overview of the influence of the pore structure on metal loading and distribution, although the field is rather descriptive. 

STRUCTURAL CHARACTERIZATION OF CARBON-SUPPORTED METAL CATALYSTS... 

Various approaches have been described in the literature for the characterization of carbon-supported metal catalysts. The catalysts are usually analyzed before and after (postmortem) their electrochemical operation with conventional ex situ techniques such as x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive x-ray analysis (EDX), x-ray photoelectron spectroscopy (XPS), and x-ray absorption spectroscopy (XAS). Although ex situ analysis provides an important starting point in catalyst characterization, one must keep in mind that significant morphological changes may occur under the operational conditions. It is thus vitally important... 

Figure 12.4 TEM images of carbon-supported metal catalysts (a,b) 20 wt% RuA ulcan XC-72 (c) 20wt% Pt-Ru(l 1)/Sibunit (Abet = 415mVg) (d) 70wt% Pt-Ru(l 1)/ Ketjenblack (e,f) 50 wt% Pt-Ru(l 1)/Sibunit (Abet = 72m /g). Insert in part (f) shows the Fourier filtered image.

The next two chapters provide a comprehensive review of carbon-supported metal catalysts and their preparation methods. The most important applications are discussed, special attention being given to the most innovative. 

Bitter JP, De Jong KP (2009) Preparation of carbon-supported metal catalysts. In Serp P, Figueiredo JL (eds) Carbon materials for catalysis. Wiley, New Jersey... 

The PTFE-bonded electrode was introduced by Neidrach and Alford [11]. It consists of metal blacks or carbon supported metal catalysts that are hydrophilic, blended with fine particles of hydrophobic PTFE, that flow and bind the structure as a result of heat treatment during fabrication. Thanks to its physical properties, PTFE flows and penetrates the pores, thus allowing a good interfacial contact between catalyst and carbon and providing hydrophobic gas pores for reactants. 

From the work (33) dealing with the carbonylation of methanol into acetic acid, it appears that the activity of carbon-supported metal catalysts follows the order Rh > Ir > Ni > Pd > Co > Ru > Fe. No significant synergic effect is observed upon the addition of a second metal to the active metallic phase. However, the use of activated carbon as a support allows to work at high temperature (250-285°C), with a stable activity over long-reaction periods (500 h) (25). 

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