Preparation of Carbon-Supported Metal Catalysts

To make effective use of the pore structure of the support, incipient-wetness impregnation can be performed in which the metal precursor is dissolved in just 

Carbon Materials for Catalysis, Edited by Philippe Serp and Josd Luis Figueiredo Copyright 2009 John Wiley Sons, Inc. 

After reviewing the literature we conclude that in all three methods—wet impregnation, incipient-wetness impregnation, and ion adsorption—two major factors govern the final dispersion of the active phase precursor-support interaction and pore structure. These two issues are discussed in the next two subsections. Note that we discuss primarily that literature which adds fundamental insights in the preparation of carbon-supported catalysts. 

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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 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. 

PtRu is the effective electrocatalyst for methanol oxidation reaction and the dispersion of the metal particles is of great importance for the utilization and activity, so we also compare several methods for the preparation of carbon-supported PtRu catalyst Similar to the reasons mentioned in Section 10.2.1 for Pt/C, high metal loadings are required for the PtRu/C catalyst We use 20wt Pt% —lOwt % Ru/C as an... 

Simonov PA, Likholobov VA. 2003. Physicochemical aspects of preparation of carbon-supported noble metal catalysts. In Wieckowski A, Savinova ER, Vayenas CG. editors. Catalysis and Electrocatalysis at Nanoparticle Surfaces. New York Marcel Decker. 

This is a topic of great practical interest because of water treatment and metal recovery applications. Its fundamental aspects are also important for the preparation of carbon-supported catalysts [22], where the catalyst precursor is typically dissolved in water prior to its loading onto the porous support. 

Physicochemical Aspects of Preparation of Carbon-Supported Noble Metal Catalysts... 

Preparation of carbon-supported noble metal catalysts (Me/C) is usually based on supporting metal precursors on carbon followed by their transformation into the metal particles. Design of an appropriate catalyst implies an optimal selection of both the support and the method of synthesis of the active component, which requires understanding the following issues ... 

The capacity of carbon support for behaving as a gas electrode and the ability of dissolved or supported metal ions, as well as the metal particles, to interact with the carbon surface through a charge transfer indicate the considerable influence of the atmosphere composition and of electrophysical properties of the carbon (the latter are determined both by the surface and hulk properties of the carbon matrix) on genesis of the supported metal catalysts. Surprisingly few papers deal with these aspects of scientific basis for preparation of Me/C catalysts. Undoubtedly, this gap should be bridged in the near future. 

Preparation of carbon-supported Pd and Au-Pd catalysts via optimized adsorption of metallic complexes... 

Electrostatic interactions between the carbon surface and the active-phase precursors have also to be taken into account in the preparation of carbon-supported catalysts. The presence of oxygen functionalities on the carbon surface, which can be produced upon the activation process (for activated carbons) and/or by subsequent oxidation treatments, renders it amphoteric. This implies that it can be more or less charged, positively or negatively, depending on the pH of the surrounding solution. Preparation variables such as the polarity of the solvent, the pH of the solution, the anionic or cationic nature of the metal precursor, and the isoelectric point (lEP) of the carbon support determine the extent of precursor-support interaction and, in this way, the total uptake and dispersion of the active phase in the final catalyst [17,20,37]. Thus, for carbons containing acidic surface groups and, as a consequence, a low isoelectric point, best results in the preparation of supported catalysts are achieved when a cationic precursor is used in basic media. Under these conditions, the acidic complexes (-COOH, -OH) are deprotonated (-COO , -0 ) in such a way that... 

Several other methods have been employed for the preparation of carbon-supported catalysts, although to a lesser extent that impregnation methods. Nakamura et al. [38] prepared molybdenum catalysts for ethene homologation by physical deposition of gaseous [Mo(CO)6]. Their supports were commercial activated carbons that were subjected to different treatments to modify then-surface. The authors compared these supports with oxidic supports and concluded that the interaction between the metal carbonyl and the carbon supports were weaker. Furthermore, they observed that oxidation of the carbon surface was effective in enhancing the catalytic activity of Mo/C, and they ascribed this effect to the contribution of the surface oxygen groups to the partial oxidation of decomposed [Mo(CO)6]. 

X-ray diffraction analysis is used routinely by every catalyst manufacturer to determine the phase composition of the catalysts produced and the size of coherently scattering domains, and hardly needs a detailed description. An aspect that we would like to emphasize concerns the influence of the enviromnent on the oxidation state of carbon-supported metal nanoparticles. Quite often, authors try to correlate electrochemical performance with the phase composition of as-prepared samples. It has, however, been demonstrated convincingly in a number of publications by both x-ray diffraction [155] and x-ray absorption spectroscopy [156] that as-prepared fuel cell catalysts and samples stored under ambient conditions are often in the form of metal oxides but are reduced under the conditions of PEMFC or DMFC operation. The most dramatic changes are observed for samples with high metal dispersions, while larger particles are affected only marginally [17]. One should keep in mind, however, that the extent of the particle oxidation depends critically on the preparation procedure. 

PtRu is the base binary catalyst for the synthesis of ternary catalysts serving as anode materials in low-temperature fuel cells. Various preparation methods of carbon supported ternary catalysts have been proposed (1) synthesis of the ternary nanoparticles, followed by deposition onto the carbon surface (one step method) (2) deposition of all the precursors on the carbon support, followed by reduction (one step method) (3) deposition of the precursor of the third metal on preformed PtRu/C, followed by reduction (two step method). Many investigations have been made to improve the performance of the PtRu binary catalysts with the incorporation of a third metal, such as W, Mo, Sn, Os, etc. 

The injection method of DP has been also applied many times for the preparation of carbon-supported noble-metal catalysts. Jin etal. [36] have deposited 5 wt% Pd on activated carbon fibers by alkaline hydrolysis of palladium chloride and obtained metal dispersions of 55-77%. Dispersions of 40-50% have been reported by Farkas ct al. [37] 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 drop-wise addition of the metal salt solution to the suspension of carbon in Na2C03 solution. In this case [38] a Pt particle size of 10 nm and a Pd particle... 

In the present article, the size and the loading efficiency of metal particles were investigated by changing the preparation method of carbon-supported platinum catalysts. First, the effect of acid/base treatment on carbon blacks supports on the preparation and electroactivity of platinum catalysts. Secondly, binary carbon-supported platinum (Pt) nanoparticles were prepared using two types of carbon materials such as carbon blacks (CBs) and graphite nanofibers (GNFs) to check the influence of carbon supports on the electroactivity of catalyst electrodes. Lastly, plasma treatment or oxyfluorination treatment effects of carbon supports on the nano structure as well as the electroactivity of the carbon supported platinum catalysts for DMFCs were studied. 

In the present study, the size and the loading efficiency of metal particles were investigated by changing the preparation method of carbon-supported platinum catalysts. Furthermore, acld/base treatment effects of carbon blacks on the nano-structure as well as the electroactivity of the carbon-supported platinum catalysts for DMFCs were studied. 

Antohni E, Salgado IRC, daSilva RM, Gonzalez ER. Preparation of carbon support binary Pt-M alloy catalysts (M=first row transition metals) by low/medium temperature methods. Mater Chem Phys 2007 101 395. 

Attwood PA, McNicol BD, Short RA. The electrocataljdic oxidation of methanol in acid electrolyte preparation and characterization of noble metal electrocatalysts supported on pre-treated carbon-fibre papers. J Appl Electrochem 1980 10 213-22. Frelink T, Visscher W, Van Veen JAR. Particle size effect of carbon supported platinum catalysts for the electrooxidation of methanol. J Electroanal Chem 1995 382 65-72. 

E.M. Crabb, R. Marshall, T. David, 2000. Carbon monoxide electro-oxidation properties of carbon supported PtSn catalysts prepared using surface organo-metallic chemistry. Journal of the Electrochemical Society, 147 4440-4447. 

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