Supported organic layer catalysts

Supported organic layer catalysts for room temperature catalytic fluorination... 

Although supported organic layer catalysts are unlikely to have commercial value they do demonstrate the importance of surface fluorination and have yielded information of value to understanding the factors that may be responsible for unwanted olefin formation in the reactions described earlier in this section. 

Room temperature ionic liquids are air stable, non-flammable, nonexplosive, immiscible with many Diels-Alder components and adducts, do not evaporate easily and act as support for the catalyst. They are useful solvents, especially for moisture and oxygen-sensitive reactants and products. In addition they are easy to handle, can be used in a large thermal range (typically —40 °C to 200 °C) and can be recovered and reused. This last point is particularly important when ionic liquids are used for catalytic reactions. The reactions are carried out under biphasic conditions and the products can be isolated by decanting the organic layer. 

Zs-3-Phenylpropenoic acid (0.025 g, 0.16 mmol), Amberlite IRA 938-supported formate (0.2 g) and Wilkinson s catalyst (0.04 g, 0.0043 mmol) were suspended in dimethylsulfoxide (0.5 ml) in a reaction tube. The mixture was irradiated with microwaves at 100 W for 30 s. On cooling, the mixture was diluted with dichloromethane (5 ml) and filtered. The filtrate was washed with water (2x5 ml). The organic layer was dried over anhydrous magnesium sulfate, the solvent removed under reduced pressure, and the residue was purified by filtration through a plug of alumina to give 3-phenylpropanoic acid (0.024 g, 95% yield). 

The right choice of a carbon support greatly affects cell performance and durability. The purpose of this chapter is to analyze how structure and properties of carbon materials influence the performance of supported noble metal catalysts in the CLs of the PEMFCs. The review chapter is organized as follows. In Section 12.2 we give an overview of carbon materials utilized for the preparation of the catalytic layers of PEMFC. We describe traditional as well as novel carbon materials, in particular carbon nanotubes and nanofibers and mesoporous carbons. In Section 12.3 we analyze properties of carbon materials essential for fuel cell performance and how these are related to the structural and substructural characteristics of carbon materials. Sections 12.4 and 12.5 are devoted to the preparation and characterization of carbon-supported electrocatalysts and CLs. In Section 12.6 we analyze how carbon supports may influence fuel cell performance. Section 12.7 is devoted to the corrosion and stability of carbon materials and carbon-supported catalysts. In Section 12.8 we provide conclusions and an outlook. Due to obvious space constraints, it was not possible to give a comprehensive treatment of all published data, so rather, we present a selective review and provide references as to where an interested reader may find more detailed information. 

Davis et al. described a new type of effective chiral catalysts, the so called "supported aqueous-phase catalysts". This hydrophilic complex is supported on a hydrophilic solid to create a large interface between the catalytic species and the organic reactants. The hydrophilicity of the ligands and the support creates an interaction sufficient to maintain immobilization of the sulfonized BINAP ligand (Scheme 7.12.) in a layer on the carrier. 

The main contaminants for the membrane are cationic species, such as metal ions, which may come from contaminated air and fuel streams when moisture is present, metal fuel cell components, balance-of-plant components, or nonmetal contaminated component materials. Other organic and inorganic materials can also contaminate the membrane, but the effects of these are less well documented. Component materials supplying contaminants may include the platinum catalyst or alloying metals, such as ruthenium or cobalt, which may leach out into the membrane the raw material source for the carbon materials (in the catalyst support, microporous layer, gas diffusion layer, or plate materials) may also have inherent metal or other chemical impurities and seal and gasketing materials, such as silicone, can decompose and contaminate the membrane. All of the membrane contaminants can also impact the ionomer materials present in the catalyst layers. 

The best example of supported aqueous phase catalysis, in which a homogeneous catalyst is embedded in an aqueous layer over silica, is the use of tetrasulfonated BINAP ligand to reduce 2-(6 -methoxy-2 -naphthyl)acrylic acid (31 Fig. 6.4). The ee is dependent on the supported organic phase, and in this case, ethylene glycol on a porous glass gave up to 95% ee for the hydrogenation product (naproxen). 

Simulations of physical properties of realistic Pt/support nanoparticle systems can provide interaction parameters that are used by molecular-level simulations of self-organization in CL inks. Coarse-grained MD studies presented in the section Mesoscale Model of Self-Organization in Catalyst Layer Inks provide vital insights on structure formation. Information on agglomerate formation, pore space morphology, ionomer structure and distribution, and wettability of pores serves as input for parameterizations of structure-dependent physical properties, discussed in the section Effective Catalyst Layer Properties From Percolation Theory. CGMD studies can be applied to study the impact of modifications in chemical properties of materials and ink composition on physical properties and stability of CLs. 

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