Carbon support-metal precursor interactions

Molecular precursors for tailored metal catalysts, 38 283-392 see also Bimetallic catalysts, cluster-derived Zeolites carbon-supported, 38 389-390 chemical interaction between clusters and supports, 38 295-296... 

The dispersion of metallic derivates on a carbon surface is dependent upon the surface properties of the carbon support. Edge carbon atoms which constitute the majority of the active surface area of graphitized carbon blacks may interact with the catalyst precursor or the catalyst itself thus providing a higher state of dispersion. 

Interaction of Metal Complexes as Catalyst Precursors with Carbon Supports and Its Influence on the State of Supported Metal Nanoparticles Produced... 

INTERACTION OF METAL COMPLEXES AS CATALYST PRECURSORS WITH CARBON SUPPORTS AND ITS INFLUENCE ON THE STATE OF SUPPORTED METAL NANOPARTICLES PRODUCED... 

Adsorption and dispersion of Pt metal precursors on carbon supports are largely influenced by the acid-base properties of the substrate and by the pH of the catalyst precursor solution [5,6]. A suitable surface-charge density on the support, in combination with the appropriate charge of the ionic precursor, favors the electrostatic interaction between the two phases, thus affecting the metal dispersion. Clearly, the surface-charge density of a carbon at a specific solution pH is determined by the acid-base behavior of the adsorption sites present on the carbon surface (Figure 1). The metal dispersion is further enhanced by the presence of... 

Adams et al. [78,79] have reported a series of synthesis of mixed-metal cluster compounds. One example, Pt2Ru4(CO)is, is depicted in Figure 1(b). This mixed cluster compound was investigated to study the effect of Pt-Ru nanoparticles developed after the precursor annealing on carbon [80]. In line with the spectroscopic and microscopic measurements, the authors demonstrated that mixed Pt-Ru nanoparticles, with an extremely narrow size distribution (particle size 1.4nm), reflect an interaction that depends on the nature of the carbon support. Furthermore, as revealed by EXAFS, the Pt-Pt, Pt-Ru, and Ru-Ru coordination distances in the precursor (2.66, 2.64, and 2.84 A) [79] changed to 2.73, 2.70, and 2.66 A, respectively, on the mixed-metal nanoparticles supported on carbon black, with an enhanced disorder [80]. Furthermore, some metal segregation could be... 

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... 

As mentioned above, the addition of promoters, and even the formation of bimetallic particles, can provide carbon-supported iron catalysts with better performances in CO hydrogenation. The method of preparation of these systems is going to determine the final effect, always taking advantage of the relative inertness of the carbon surface. The interaction between the different components of the active phase can be maximized by using mixed-metal carbonyl complexes. Furthermore, use of these precursors allows for the preparation of catalysts with... 

The interaction of a metal precursor with carbon supports is known to affect the physical and chemical properties of (he supported metal catalysts. To study the interaction, it is necessary to answer the foRowing questions (i) what is the chemical nature of this interaction, (ii) what role do physical and chemical properties of the support play in this case, (iii) which peculiarities of the process determine the statie and catalytic behaviour of the active component of the catalyst. 

Roman-Martinez, M. et al. 1995. Metal-support interaction in Pt/C catalysts. Influence of the support surface chemistry and the metal precursor. Carbon 33 3-13. 

---