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Here we report novel catalysts for nitrobenzene hydrogenation based on Ru/RuO 2 nanoparticles (NPs) and including iron oxide NPs, allowing magnetic recovery. The solvent type, reaction temperature, and the size and composition of initial iron oxide NPs are demonstrated to be the control factors determining synthesis outcomes including the degree of NP aggregation and catalytic properties. A complete characterization of the catalysts using transmission electron microscopy (TEM), X-ray powder diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and energy dispersive x-ray spectroscopy (EDS) allowed assessment of the structure-property relationships. It is revealed that coexistence of the Ru/RuO 2 and iron oxide NPs in the catalyst as well as the proximity of two different NP types lead to significantly higher aniline yields and reaction rates. The catalytic properties are also influenced by the type of iron oxide NPs present in the catalytic samples.

Here we report control of iron oxide and palladium nanoparticle (NP) formation via stabilization with polyphenylenepyridyl dendrons of the second and third generations with dodecyl periphery. These nanomaterials are developed as magnetically recoverable catalysts. To accurately assess the influence of the dodecyl exterior for the same dendron generation, we also designed a second generation dendron with partial dodecyl periphery. For all dendrons studied, the multicore iron oxide mesocrystals were formed, the sizes and morphology of which were controlled by the dendron generation. Analysis of the static and dynamic magnetic properties, in combination with transmission electron microscopy observations, demonstrate that magnetism is sensitive on the structure-directing capabilities of the type of the dendron which was employed for the mesocrystal stabilization. Close proximity of single cores in such multicore mesocrystals promotes the coupling of the neighboring magnetic moments, thus boosting their magnetization and allowing easy crossover between superparamagnetic and ferrimagnetic behaviors at room temperature. The particularly dramatic role of the dendron structure was also witnessed via the Pd NP formation, which was found to depend on both the dendron generation and its dodecyl periphery. In the case of the catalyst based on the second generation dendron with full dodecyl periphery, no Pd NPs were observed by TEM indicating that these species are of a subnanometer size and are not visible on or near the iron oxide NPs. For the catalyst based on the second generation dendron with partial dodecyl periphery, hydrogen reduction leads to much larger Pd NPs (2.7 nm) due to an unimpeded exchange of Pd species between dendrons and nondense dendron coating with asymmetrical dendrons. The third generation dendron with full dodecyl periphery allows nearly monodisperse 1.2 nm Pd NPs in the shells of iron oxide mesocrystals and the best catalytic properties in selective hydrogenation of dimethylethynylcarbinol. This study suggests a robust approach to control NP formation in magnetically recoverable catalysts for a wide variety of catalytic reactions using dendrons combining rigidity and flexibility in one molecule.

The properties of enzymatic systems based on horseradish root peroxidase immobilized on magnetic particles were studied. Magnetic Fe3O4 nanoparticles were synthesized by co-precipitation. Then, horseradish root peroxidase was immobilized on their surface in two ways by covalent crosslinking. For this purposes, in the first case, Fe3O4 was sequentially treated with tetraethoxysilane, 3-minopropyltriethoxysilane, glutaraldehyde and HRP. In the second case, before immobilization of HRP, 3-minopropyltriethoxysilane, glutaraldehyde and HRP were sequentially deposited onto the support surface. The activity of the synthesized biocatalysts was evaluated spectrophotometrically in the oxidation reaction of 2,2’-azino-bis (3-ethylbenzothiazolin-6-sulfonate) ammonium with hydrogen peroxide. The kinetic parameters K m and V max were also calculated for all types of catalysts, including native HRP. Among all biocatalytic systems, the best values, compared with the native enzyme (K m = 4 mmol/L and V max = 12.6 · 10−4, mmol/L·s), were obtained for the first type of biocatalyst (K m = 5 mmol / L and V max = 2.5 · 10−4, mmol/L·s). It was also determined that the optimum pH is 7.2.

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