Hydrogenation with Catalytic Nanoparticles

The catalytic lifetime was studied by reusing the aqueous phase for three successive hydrogenation runs of toluene, anisole and cresol. Similar turnover activities were observed during the successive runs. These results show the good stability of the catalytically active iridium suspension as previously described with rhodium nanoparticles. 

The synthesis of Pd/ACF (0.42wt.% Pd) catalyst with monodispersed nanoparticles carried out at cuo = 3 is illustrated, as well as its catalytic performance in a liquid-phase hydrogenation of 1-hexyne in comparison with a traditional powdered Lindlar catalyst. 

Table 9.12 Catalytic hydrogenation of olefins with Pd nanoparticles in a water-in-hexane microemulsion. (Reprinted with the permission of the American Chemical Society [79])...

Iridium nanoparticles generated in l-n-butyl-3-methylimidazolium (BMI)-based ionic liquids were found to be excellent recyclable catalytic systems for the hydrogenation of a variety of substrates, including ketones such as simple ketones. The Ir nanoparticles were prepared by simple reduchon of [Ir(cod)Cl]2 dispersed in BMI-PFis at 75 °C under 4 atm of H2. Benzaldehyde, cyclopentanone, methyl butanone and derivatives were hydrogenated with almost complete conversion, with TOFs ranging from 17 to 96h under solventless conditions (substrate Ir ratio = 250, 75 °C, 4 atm FI2) [102]. 

When the hydrogenation of citral is performed with supported nanoparticles of rhodium metal, for example Rh/Si02 under classical conditions [liquid phase, rhodium dispersion 80% (particles in the range of 1-2nm), citral/Rhs = 200, P(ti2) = 80bar, T = 340 K], the catalytic activity is very high but most of the above products are obtained and the reaction is totally non-selective, even if the major product was citronellal. 

The possibility of the incorporation of oxygen into the particle is particularly relevant for the carbides and nitrides of molybdenum and tungsten which possess a high affinity for this element.13,23 The oxygen may come from the carbonyl precursor, and result in oxycarbide or oxynitride formation in the core of the nanoparticle itself.16 Exposure to the ambient can also result in the formation of surface oxycarbides and oxynitrides with catalytic properties different from those of the pure nitride or carbide phase.15,24-26 However, heat treatment of these nanoparticles with a mixture of methane/hydrogen or ammonia/hydrogen should convert the surface to a pure nitride or carbide form. 

Catalytic hydrogenation of alkenes and aUc3mes is achieved with nickel nanoparticles prepared from NiCl2 by reduction with Li and catal)dic amounts of DTBB and an alcohol. ... 

Unlike regular block copolymer micelles which are well permeable for reagents, triblock nanospheres with hydroxylated polyisoprene coronas, cross-linked poly(2-cinnamoyloxyethyl methacrylate) shells, and poly(acrylic acid) cores, filled with Pd nanoparticles, showed slower hydrogenation of alkenes than Pd blacks due to the need for the reactant(s) to diffuse into and the products to diffuse out of the encapsulating nanospheres [13]. On the other hand, microspheres formed by diblock poly(t-butyl acrylate)-hlocfe-poly(2-cinnamoyloxyethyl methacrylate) and filled with Pd nanoparticles demonstrated good permeability and higher catalytic activity in the hydrogenation of methyl methacrylate than the commercial Pd black catalyst [14]. 

Por the computation we have used the integral method using cubic spline and the combined gradient method of Levenberg-Marquardt [57, 58]. The kinetic models chosen describe well the hydrogenation kinetics. In the formulas presented in Table 3.1 k is the kinetic parameter of the reaction and Q takes into account the coordination (adsorption) of the product (LN) and substrate (DHL) with the catalyst (the ratio of the adsorption-desoprtion equilibrium constants for LN and DHL). Parameters of the Arrhenius equation, apparent activation energy kj mol , and frequency factor k, have been determined from the data on activities at different temperatures. The frequency factor is derived from the ordinate intercept of the Arrhenius dependence and provides a measure of the number of collisions or active centers on the surface of catalytic nanoparticles. 

TABLE 12.4 Catalytic Hydrogenations of Organic Compounds With Pd Nanoparticles Stabilized in Water-in-C02 Microemulsions... 

The influence of CO2 pressure on catalytic activity and product distribution of the aqueous core of the microemulsion droplet with different nanoparticles guests (Pd and Ru) prepared in situ was investigated by varying the pressure of CO2 while keeping the hydrogen pressure constant (Fig. 12.4) [48]. 

Ohde M, Ohde H, Wai CM. Catalytic hydrogenation of arenes with rhodium nanoparticles in a water-in-supercritical CO2 microemulsion. Chem Commun 2002 2388-9. 

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