Milan Králik

Catalysis by metal nanoparticles supported on functional organic polymers

Abstract The preparation and catalytic applications of dispersed metal catalysts supported on organic functional polymers are presented. The advantages of these catalysts, such as the easy tailoring with respect to the nature of the used support, the “nanoscale” size control of metal crystallites by the polymer framework, the high accessibility and consequent catalytic activity in a proper liquid or liquid–vapor reaction systems are stressed. Various proposed catalytic processes making use of these materials are presented and evaluated, including multifunctional catalysis, e.g. redox-acid. Interesting peculiar aspects such as the enhancement of the hydrogenation rate by nitrogen containing moieties anchored to the polymer backbone are emphasised. When suitable, a comparison with catalysts based on inorganic supports is given.

Generating palladium nanoclusters inside functional cross-linked polymer frameworks

The use of functional resins as designable supports for palladium nanoclusters is reviewed. Data are related to the generation of Pd nanoparticles under various conditions and inside gel-type or macroporous frameworks. The combination of different physico-chemical techniques (ISEC, ESR and PGSE NMR) is illustrated as a powerful tool for evaluating nanomorphology and molecular accessibility, mainly of gel-type resins. A few examples of catalytic applications are presented and discussed and prospects for wider utilizations are evaluated.

Hydrogenation of benzene to cyclohexene over polymer-supported ruthenium catalysts

Abstract Partial liquid-phase hydrogenation of benzene to cyclohexene over ruthenium catalysts supported on charcoal and anionic cross-linked polymers is described. The influence of the polarity of polymeric supports, nature of the solvent and the presence of zinc additives on the performance of the catalyst in a glass-lined reactor at 100–110°C and a pressure of 1.5 MPa have been studied. It has been found that at 42–47% conversion of benzene, the selectivity to cyclohexene, observed in water with Ru catalysts supported on a strongly hydrophilic microporous resin, is higher than that displayed by Ru supported on charcoal. The effect of water on the performance of the catalyst is probably a result of formation of a suitable environment around Ru particles and of a good accessibility of metal particles dispersed within the hydrophilic polymer support.

Functional resins as innovative supports for catalytically active metal nanoclusters

Functional resins are plausible candidates for supporting catalytically active metal nanoclusters alternative, or complementary to conventional supports such as amorphous carbon, metal oxides, zeolites. Mechanical and thermal stabilities are fair and perfectly suitable to application in the realm of fine chemistry. The polymer framework turns out to be a designable template for controlling nanoclusters size and size distributions.

Microporous poly-N,N-dimethylacrylamide-p-styrylsulfonate-methylene bis(acrylamide): a promising support for metal catalysis

Abstract The synthesis of poly- N,N -dimethylacrylamide- p -styrylsulfonate (DMAA-SS) with 4 mol% of methylene bis(acrylamide) mol% of methylene bis(acrylamide) (MBAA) as crosslinker is described. Bulk polymerization of water solution of monomers (DMAA, SS sodium salt, MBAA) was carried out under gamma irradiation. Swellability in water and various organic solvents showed mainly hydrophilic character of the resin. The ion-exchange experiments with 1 M hydrochloric acid and with [Pd(NH 3 ) 4 ] 2+ showed very good accessibility of the inner space of the material. Polymer supported [Pd(NH 3 4 ] 2+ was reduced by hydrogen in methanol, sodium borohydride in water and sodium borohydride in ethanol. Under these last conditions uniform distribution of Pd throughout the resin particles was observed. The activated material turned out to be a good catalyst for the hydrogenation of p -nitrotoluene to p -toluidine in methanol under ambient conditions.

Relationships between physico-chemical properties and catalytic activity of polymer-supported palladium catalysts.: Part I. Experimental investigations

Abstract Polymer-supported palladium catalysts based on microporouspolydimethylacrylamide- p -styryl-sulphonate-methylenebis(acrylamide) with 4 and 8% m/m crosslinking degree and various metal contents were prepared. The influence of the crosslinking degree on the metal distribution and on the final activity of the catalyst was studied by a combination of diverse physico-chemical techniques like X-ray microprobe analysis, inverse steric exclusion chromatography, powder X-ray diffraction, electron spin resonance, and catalytic tests.

Relationships between physico-chemical properties and catalytic activity of polymer-supported palladium catalysts II. Mathematical model

Abstract A mathematical model including external mass transport, diffusion in the particle and chemical reaction inside the particle was developed to describe a hydrogenation process in an isothermal batchwise system with a polymer-supported metal catalyst. Various types of reaction kinetics were implemented into the model, e.g., the power law or the Langmuir-Hinshelwood type. The validity of the model was tested on data obtained from the hydrogenation of a 1 M methanol solution of cyclohexene at 25°C and 0.5–1.5 MPa. Diffusional coefficients inside the catalyst, the hydrogenation rate constant and the adsorption constant of hydrogen were estimated. The best model proved to be the model considering the dissociation of hydrogen and neglecting the adsorption terms in the denominator of the Langmuir-Hinshelwood kinetics. Using polymer supports of different swellability, a linear correlation between the logarithm of the diffusional coefficient of a solute inside the polymer and the reciprocal of the swelling volume of the polymer support was derived from ESR measurements. A comparison with values of diffusional coefficients obtained from catalytic tests confirmed the validity of this correlation.

Metal palladium supported on amphiphilic microporous synthetic organic supports. Part I. Material preparation and textural characterization

Abstract Styrene, 2-methacryloxyethylsulfonic acid and methylenebisacrylamide are copolymerized in the presence of dimethylformamide under γ -irradiation at room temperature to give potentially amphiphilic, microporous resins. The molar fraction of methylenebisacrylamide (the cross-linker) ranges from 1 to 6 mol%. The obtained resins, after grinding and sieving, are treated with solutions of Pd(AcO) 2 and the ion-exchanged polymers are then treated with NaBH 4 in ethanol. The metal content in the materials ranges from 2.1% to 2.4% (w/w). X-ray microprobe analysis shows that Pd(0) is homogeneously dispersed throughout the particles of the polymeric materials. The polymer chain concentration and its distribution in the swollen macromolecular networks are assessed by means of Inverse Steric Exclusion Chromatography (ISEC). In spite of the higher molar proportion of styrene repeating units, the Pd(0)-resin composites swell comparably in water and tetrahydrofurane. Their amphiphilic character is the result of the different swelling properties of the hydrophilic and hydrophobic domains.

Highly Chemoselective Hydrogenation of 2-Ethylanthraquinone to 2-Ethylanthrahydroquinone Catalyzed by Palladium Metal Dispersed inside Highly Lipophilic Functional Resins

Most hydrogen peroxide is currently produced by the selective hydrogenation of 2-ethylanthraquinone (EAQ) to 2-ethylanthrahydroquinone (EAHQ), followed by treatment with dioxygen; this produces hydrogen peroxide and regenerates 2-ethylanthraquinone. We have developed novel catalysts for this process that are based on palladium supported on very lipophilic functional resins and that are able to promote a chemoselectivity for EAHQ slightly but definitely superior to that provided by an industrial catalyst under identical conditions. This finding demonstrates the potential of variations of the lipophilic/hydrophilic character of the support as a tool for the improvement of the chemoselectivity of resin-based metal catalysts.

Polymer frameworks as templates for generating size-controlled metal nanoclusters Active and reusable metal catalysts based on organic resins and on organic/inorganic composites

Abstract Catalysts based on Pd nanoparticles supported on polyacrylic resins or on polyacrylic resins/silica composites are evaluated in terms of catalyst reusability and mechanical stability. Both technologically relevant features are satisfactory. Resin/silica/Pd composites exhibit an appreciable but not dramatic decrease of specific catalytic activity (3–4 times) when compared with their parent resin/Pd materials, but this decrease is compensated by higher mechanical stability and easier separability of the catalyst from the reaction mixture.