Supports for Platinum Catalysts

The value of oxidized nichrome as a support for platinum catalysts has also been explored by a group of workers (26,126,177). 

Coloma F, Sepulveda Escribano A, Rodriguez Reinoso F (1995) Heat-treated carbon-blacks as supports for platinum catalysts. J Catal 154 299-305... 

There are several advantages for the use of S-ZrOj as a catalyst support in PEMFC applications. Because of its hydrophilicity, it has been suggested that this type of fuel cell catalyst would be well suited for low-relative humidity conditions and possibly simplify fuel cell components to operate without the use of a humidifier. Due to the proton conductivity across the surface of the material, less Nafion iono-mer needs to be cast to form the TPBs. Platinum utilization increases as the S-ZrOj support acts as both the platinum and proton conductor and better gas diffusion to the catalyst site results from the decreased blockage of Nafion ionomer (Liu et al., 2006a,b). It is beheved that within porous carbon catalyst supports, platinum deposited within the pores may not have proton conductivity due to the perfluorosul-fonated ionomer unahle to penetrate into the pores. Thus, a TPB which is necessary for a catalyst active site will not be formed. Therefore, the S-ZrOj support has an additional benefit over porous carbon material supports in that by using the S-ZrOj as a support for platinum catalysts, the surface of the support can act as a proton conductor and platinum deposited anywhere on the surface of the support will provide immediate access to the electron and proton pathways thereby requiring less Nafion. Thus the use of S-ZrOj in fuel cell MEA components may potentially lower the cost of materials substantially, as the catalytic metals and membrane materials are among the most costly in a PEMFC. However, like most metallic oxides, the downside of their use stems from their relatively low electron conductivity and low surface areas that results in poor platinum dispersion. 

An appreciable increase in the utilization efficiency of platinum catalysts in fuel cells was attained when the highly dispersed platinum was deposited not directly onto the conductive electtode base but onto carbon black or other carbon materials serving as an intermediate base for the nanodispersed catalyst. On carbon supports, the nanosized platinum crystallites were less subject to recrystallization and coarsening. In addition, new technical devices such as adding Nafion ionomer to the active mass have helped to considerably improve the contact between catalyst and solid electrolyte (a Nafion-lype membrane). Carbon black was found to be a very convenient support for platinum catalysts. It is readily available and not expensive. Certain blacks (such as furnace black Vulcan XC-72) have special surface properties that have a favorable effect on catalyst activity. 

In recent years, carbon nanotubes (CNTs) have received attention as supports for platinum catalysts. They have an internal diameter of 3 to 10 nm, an external... 

An electronic conductive polymer was found by Strike al. as a support for platinum with a co-catalysts. The platinum particles were deposited on electrodeposited polypyrrole. 

C. Micheaud, P Marecot, M. Guerin, and J. Barbier, Reparation of alumina supported palladium-platinum catalysts by surface redox reactions Activity for complete hydrocarbon oxidation, Appl. Catal. A 171, 229-239 (1998). 

Finally, clays can be used as supports for other catalysts such as platinum metal or aluminum chloride, largely to facilitate recovery of the catalyst from a liquid after reaction (e.g., by filtration). 

There are more than 50 natural and well over 100 synthetic zeolites, the latter all made by hydrothermal synthesis. The main uses are as molecular sieves and catalyst supports for platinum group and other metals.49... 

A different way of making electrolytic reduction is through electrocatalytic hydrogenation, which is a kind of indirect electrolysis. Protons are reduced and the key intermediate is Me(H) (with Me being platinum, palladium, rhodium, or nickel), and the potential determining step is the formation of this reactive intermediate. Selective reductions may be performed by this method, and the potential used for the formation of Me(H) is often less negative than that required for the direct electron transfer to the reducible substrate. Hence, electrolysis occurs with a lower energy consumption. The selectivity of the reaction may depend on the support for the catalyst. 

Little is known about the chemical nature of the recently isolated carbon clusters (C o> C70, Cg4, and so forth). One potential application of these materials is as highly dispersed supports for metal catalysts, and therefore the question of how metal atoms bind to C40 is of interest. Reaction of C o with organometallic ruthenium and platinum re nts has shown that metals can be attached directly to the carbon framework. Ihe native geometry of transition metal, and an x-ray difi action analysis of the platinum complex [(CgHg)3P]2Pt( () -C6o) C4HgO revealed a structure similar to that known for [(C4Hs)3P]2Pt( n -ethylene). The reactivity of C40 is not like that of relatively electron-rich planar aromatic molecules su( as benzene. The carbon-carbon double bonds of C40 react like those of very electron-deficient arenes and alkcnes. 

Functionalised Polymer Fibres as Supports for Platinum Group Metal Catalysts... 

Richard et al. studied a model Pt/Al203 catalyst by transmission electron microscopy and Auger electron microscopy. Oxygen treatments under industrial catalyst regeneration conditions transform a monomodal distribution of platinum particles (mean diameter 1.8 nm) into a bimodal distribution consisting of a phase of particles 10 to 40 nm in diameter and a phase of very small clusters (diameter <1 nm). This observation of stable small clusters is direct evidence for platinum catalyst support interaction. An exchange of water between particles that operate on a molecular scale and might include platinum oxide is postulated. 

Group VIII metals supported on silica are known to hydrogenate preferentially the C=C double bond of a,B-unsaturated aldehydes (as e.g. crotonaldehyde). Only for a few metals, like Os and Co, a significant activity for the hydrogenation of the C=0 group was reported [1]. Improved selectivity for carbonyl group hydrogenation was described for platinum catalysts modified by Sn [2,3,4], Fe... 

However, the reverse order was observed for platinum catalysts also for the oxidation of methane [51]. The acidic properties of the support are of prime importance, with solid superacids showing high activity at relatively low temperatures [49]. Ishikawa and co-workers have found that in the oxidation of... 

Schmitt, Jr., J. L., and P. L. Walker, Jr. 1971. Carbon molecular sieve supports for metal catalysts-I. Preparation of the system platinum supported on polyfiirfuryl alcohol Carbon. Carbon 9 791-796. 

Studies already published in the literature report that a higher activity for platinum catalysts supported on zeolites compared with y-Al203 supported catalysts (Katzer, 1977). In addition, the reactions of ethylbenzene through routes of isomerization, transalkylation, and disproportionation are reported as preferred. 

Xia, W, Bron, M, Schuhmann, W., and Muhler, M (2012) Synthesis of an improved hierarchical carbon-fiber composite as a catalyst support for platinum and its application in electrocatalysis. Carbon, 50, 4534—4542. 

Liu Y, Mustain WE (2012) Evaluation of tungsten carbide as the electrocatalyst support for platinum hydrogen evolution/oxidation catalysts. Int J Hydrogen Energy 37(ll) 8929-8938... 

Kim, S. Park, S.-J. (2006). Effects of chemical treatment of carbon supports on electrochemical behaviors for platinum catalysts of fuel cells. J. Power Sources, 159, 42-45. 

Inert metals such as platinum have been used as a support for palladium catalyst through a putative metal-metal bond resembling those present in metal clusters. There have been numerous reports concerning the use of various zeofites as support for palladium catalysts.f Palladium complexes entrapped into zeolite cages have been reported to be reusable catalyst for the Heck reaction, without the difficulties associated with cage diffusion problems. " ... 

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