Catalyst supports colloidal polymers

It was recently reported that the colloidal Pt nanoparticles may be protected by glycol, which serves as both a solvent and the protecting agent [71, 102]. For example, Kongkanand and co-workers [102] used ethylene glycol as a reducing agent to prepare well-dispersed Pt catalysts supported by polymer-wrapped CNTs. In their procedure, the CNTs were sonicated in A,7V-dimethyIformamide for 15 h to break up the nanotube bundles into individual CNTs. However, polymer such as... 

Polymer-supported catalysts often have lower activities than the soluble catalysts because of the intraparticle diffusion resistance. In this case the immobilization of the complexes on colloidal polymers can increase the catalytic activity. Catalysts bound to polymer latexes were used in oxidation reactions, such as the Cu-catalyzed oxidation of ascorbic acid,12 the Co-catalyzed oxidation of tetralin,13 and the CoPc-catalyzed oxidation of butylphenol14 and thiols.1516 Mn(III)-porphyrin bound to colloidal anion exchange resin was... 

A variety of compounds has been reduced employing colloidal palladium catalysts supported by synthetic polymers. Table I summarizes the results of various reductions (13). 

Frolov, Shabanova, and co-workers (37-39) studied the transition of a sol into a gel and the aggregate stability of colloidal silica. Their aim was to develop a technology for the production of highly-concentrated silica sols and to use them as binders, catalyst supports, polymer fillers, adsorbents, and so forth. Kinetic studies were made of polycondensation and gel formation in aqueous solutions of silicic acids. At the stage of particle growth, poly condensation proceeds in the diffusion-kinetic region. With changes in pH, temperature, concentration, and the nature of electrolytes,... 

The author s own interest in this area includes new functional polymers for solid phase synthesis [11-13], polymers with molecularly imprinted substrate selectivity [14], polymer-supported transition metal catalysts [15], novel polymers of potential interest for electrocatalysis [16], targeting of colloidal drug carriers [17, 18], molecular composites [19], and biocompatible surfaces [20]. These studies have led to, among other things, a uniquely versatile method of polymer synthesis based on the chemistry of activated acrylates, i.e. polymer synthesis via activated esters. Various aspects of polymers and copolymers of activated (meth)acrylates have also been investigated in this and several other laboratories. 

This chapter will only deal with catalytic systems covalently attached to the support. Dendrimer [96-101], hyperbranched polymer [102, 103], or other polymer [100] encapsulated catalysts, micellar catalysis [104] and non-cova-lently bound catalysts (via ionic [105,106], fluorous, etc. intercations) are not being treated. Also catalysis with colloidal polymers [ 107,108] and biocatalysts, such as enzymes and RNA, will not be reviewed here. 

It was found that for enantioselective hydrogenation over modified platinum catalysts the most suitable SC-solvents are ethane and propane as indicated in Table 5.15. Application of SC-CO2 in hydrogenation on chiral modified Pt-catalysts proved to be less suitable because CO2 is partly hydrogenated into CO, which poisons the catalyst But polymer-supported colloidal Pd nanoparticles as catalysts in supercritical CO2 (SCCO2) revealed top s as high as 4 x 10 h" at 15 bar hydrogen, and 50°C (Niessen et al. 

Zhang S, Chen L, Zhou S, Zhao D, Wu L (2010) Facile synthesis of hierarchically ordered porous carbon via in situ self-assembly of colloidal polymer and silica spheres and its use as a catalyst support. Chem Mater 22 3433-3440... 

Polymer colloids as catalyst supports and for metal-complexing... 

Recently, Chaudhari compared the activity of dispersed nanosized metal particles prepared by chemical or radiolytic reduction and stabilized by various polymers (PVP, PVA or poly(methylvinyl ether)) with the one of conventional supported metal catalysts in the partial hydrogenation of 2-butyne-l,4-diol. Several transition metals (e.g., Pd, Pt, Rh, Ru, Ni) were prepared according to conventional methods and subsequently investigated [89]. In general, the catalysts prepared by chemical reduction methods were more active than those prepared by radiolysis, and in all cases aqueous colloids showed a higher catalytic activity (up to 40-fold) in comparison with corresponding conventional catalysts. The best results were obtained with cubic Pd nanosized particles obtained by chemical reduction (Table 9.13). 

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