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The growing demand for new energy sources governs the intensive research into CO2 hydrogenation to methanol, a valuable liquid fuel. Recently, indium-based catalysts have shown promise in this reaction, but they are plagued by shortcomings such as structural instability during the reaction and low selectivity. Here, we report a new strategy of controlling the selectivity and stability of bimetallic magnetically recoverable indium-based catalysts deposited onto a solid support. This was accomplished by the introduction of a structural promoter: a branched pyridylphenylene polymer (PPP). The selectivity of methanol formation for this catalyst reached 98.5%, while in the absence of PPP, the catalysts produced a large amount of methane, and the selectivity was about 70.2%. The methanol production rate was higher by a factor of twelve compared to that of a commercial Cu-based catalyst. Along with tuning selectivity, PPP allowed the catalyst to maintain a high stability, enhancing the CO2 sorption capacity and the protection of In against sintering and over-reduction. A careful evaluation of the structure–activity relationships allowed us to balance the catalyst composition with a high level of structural control, providing synergy between the support, magnetic constituent, catalytic species, and the stabilizing polymer layer. We also uncovered the role of each component in the ultimate methanol activity and selectivity. [ABSTRACT FROM AUTHOR]

Development of new microporous organic polymers attracts significant attention due to a wide scope of promising applications. In addition, the synthesis of soluble, non-crosslinking polymers of high surface area and uniform microporosity is very challenging, and the methods for soluble microporous polymers formation are rather limited. In this work, we report a new approach to construct porous polyphenylenes which employs the Diels–Alder polycondensation of multifunctional ethynyl-containing monomers of different spatial architecture with bis(cyclopentadienone)s. The resulting polymers were soluble in common organic solvents, and their structure and properties were assessed by NMR, TGA, DSC, and SEC studies. The polymers demonstrated a specific surface area up to 751 m2·g−1 and ultramicroporous (pore size ≤ 0.6 nm) structure. N2 and CO2 adsorption–desorption data revealed that porosity parameters, e.g., specific surface area and pore sizes, can be tuned selectively by varying the type of monomers and reaction conditions. [ABSTRACT FROM AUTHOR]

CO2 hydrogenation to methanol is an important process that could solve the problem of emitted CO2 that contributes to environmental concern. Here we developed Cr-, Cr-Zn-, and Cr-Ni-containing nanocomposites based on a solid support (SiO2 or Al2O3) with embedded magnetic nanoparticles (NPs) and covered by a cross-linked pyridylphenylene polymer layer. The decomposition of Cr, Zn, and Ni precursors in the presence of supports containing magnetic oxide led to formation of amorphous metal oxides evenly distributed over the support-polymer space, together with the partial diffusion of metal species into magnetic NPs. We demonstrated the catalytic activity of Cr2O3 in the hydrogenation reaction of CO2 to methanol, which was further increased by 50% and 204% by incorporation of Ni and Zn species, respectively. The fine intermixing of metal species ensures an enhanced methanol productivity. Careful adjustment of constituent elements, e.g., catalytic metal, type of support, presence of magnetic NPs, and deposition of hydrophobic polymer layer contributes to the synergetic promotional effect required for activation of CO2 molecules as well. The results of catalytic recycle experiments revealed excellent stability of the catalysts due to protective role of hydrophobic polymer. [ABSTRACT FROM AUTHOR]

Hydrodynamic and optical methods were applied to study conformational and physical properties of hyperbranched pyridylphenylene polymers in dilute solutions. The samples were synthesized using Diels-Alder polycyclocondensation. It was demonstrated that hydrodynamic properties of the studied macromolecules were typical for compact non-percolated spheres. Optical and electro-optical methods revealed information regarding the shape and asymmetry of the macromolecules ( p ≈ 1.4). The contributions of optical shape effect to the observed flow birefringence of polypyridylphenylene solutions and intrinsic anisotropy of polarizability were evaluated and analysed. It was shown that varying the polymer composition (i.e. the degree of branching) caused considerable changes in the anisotropy of optical polarizability of the polymers. Dramatic difference of the electro-optical properties in non-polar (toluene) and polar (tetrachloroethane) solvents was found; this difference was related to the orientational correlation of polar solvent molecules with respect to the macromolecules. Dynamic properties were studied by non-equilibrium electric birefringence which had a reasonable agreement with the dimensions estimated from hydrodynamic data. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Herewe report control of iron oxide and palladium nanoparticle (NP) formationvia stabilization with polyphenylenepyridyl dendrons of the secondand third generations with dodecyl periphery. These nanomaterialsare developed as magnetically recoverable catalysts. To accuratelyassess the influence of the dodecyl exterior for the same dendrongeneration, we also designed a second generation dendron with partialdodecyl periphery. For all dendrons studied, the multicore iron oxidemesocrystals were formed, the sizes and morphology of which were controlledby the dendron generation. Analysis of the static and dynamic magneticproperties, in combination with transmission electron microscopy observations,demonstrate that magnetism is sensitive on the structure-directingcapabilities of the type of the dendron which was employed for themesocrystal stabilization. Close proximity of single cores in suchmulticore mesocrystals promotes the coupling of the neighboring magneticmoments, thus boosting their magnetization and allowing easy crossoverbetween superparamagnetic and ferrimagnetic behaviors at room temperature.The particularly dramatic role of the dendron structure was also witnessedvia the Pd NP formation, which was found to depend on both the dendrongeneration and its dodecyl periphery. In the case of the catalystbased on the second generation dendron with full dodecyl periphery,no Pd NPs were observed by TEM indicating that these species are ofa subnanometer size and are not visible on or near the iron oxideNPs. For the catalyst based on the second generation dendron withpartial dodecyl periphery, hydrogen reduction leads to much largerPd NPs (2.7 nm) due to an unimpeded exchange of Pd species betweendendrons and nondense dendron coating with asymmetrical dendrons.The third generation dendron with full dodecyl periphery allows nearlymonodisperse 1.2 nm Pd NPs in the shells of iron oxide mesocrystalsand the best catalytic properties in selective hydrogenation of dimethylethynylcarbinol.This study suggests a robust approach to control NP formation in magneticallyrecoverable catalysts for a wide variety of catalytic reactions usingdendrons combining rigidity and flexibility in one molecule. [ABSTRACT FROM AUTHOR]

Forthe first time we report syntheses of a family of functionalpolyphenylenepyridyl dendrons with different generations and structuressuch as focal groups, periphery, and a combination of phenylene andpyridyl moieties in the dendron interior using a Diels–Alderapproach and a divergent method. The dendron structure and compositionwere confirmed using NMR spectroscopy, MALDI-TOF mass spectrometry,FTIR, and elemental analysis. As a proof of concept that these dendronscan be successfully used for the development of nanocomposites, synthesisof iron oxide nanoparticles was carried out in the presence of thermallystable dendrons as capping molecules followed by formation of Pd NPsin the dendron shells. This resulted in magnetically recoverable catalystsexhibiting exceptional performance in selective hydrogenation of dimethylethynylcarbinol(DMEC) to dimethylvinylcarbinol (DMVC). [ABSTRACT FROM AUTHOR]