Figure 4. Dendrimer nanotemplating in aqueous solution.In a first step, the dendrimer is loaded with a precursor salt (H + AuCl 4 À ), resulting in a charged dendrimer with the precursor as counterions. In a second step, the chemical reduction is performed, which yields a colloid inside the dendrimer. Reprinted with permission from ref 110.

Nanoparticle (NP)/polymer nanocomposites received considerable attention because of their important applications including catalysis. Metal and metal oxide NPs may impart catalytic properties to polymer nanocomposites, while polymers with a different structure, functionality, and architecture control the NP formation (size, shape, location, composition, etc.) and in this way, govern catalytic properties of nanocomposites. In this review we will discuss the influence of the polymer nanostructure (thin or grafted layers, polymer ordering, polymer nanopores), architecture (branched vs linear), functional groups (coordinating or ionic), specific properties (reducing, stimuli responsive, conductive), etc. on the formation of metal or metal oxide NPs and the catalytic behavior of the nanocomposites. The development of novel and efficient catalysts is crucial for progress in chemical sciences, and this explains a huge number of publications in this area in recent years. Taking into consideration previous review articles on NP/polymer catalysts, we limited this review to a discussion of a narrow temporal scope (2017–April 2019), while embracing a broad subject scope, i.e., considering any polymers and NPs which form catalytic nanocomposites. This gives us a unique view of the field of catalytic polymer nanocomposites and allows understanding of where the field is going.

A new family of poly(phenylene-pyridyl) dendrimers (up to the fourth generation) with different periphery was synthesized via a divergent route by using a cascade of Diels-Alder cycloadditions. Tetra(4-ethynylphen-1-yl)methane served as a core. A new A 2B cyclopentadienone building block, namely, pyridine-containing cyclopentadienone with protected dienophile functions was prepared. By varying the building blocks at the last step of dendrimer construction, one could design molecules possessing either a phenyl-or a pyridyl-decorated outershell. The products were characterized by NMR spectroscopy, MALDI-TOF mass spectrometry, elemental analysis, atomic force microscopy, thermogravimetric analysis, DSC, and dynamic light scattering methods. These stiff polyphenylene dendrimers with pyridine embeds were then used as a matrix for encapsulation of Pd nanoparticles. The fourth-generation poly(phenylenepyridyl) dendrimer with a phenyl-decorated periphery and pyridine-containing interior was found to serve as a powerful template for metal nanoparticle formation, resulting in excellent nanoparticle stability (no precipitation was observed for more than 6 months).

Diels−Alder reactions between 1,4-bis(2,4,5-triphenylcyclopentadienone-3-yl)benzene and either phenylacetylene (model reaction) or 1,4-diethynylbenzene (polymer formation) were studied. NMR spectra suggest that the main product in the model reaction is the m,m-isomer (up to 83% yield). X-ray crystal structure analysis convincingly proved the structure of the above isomer. The polymer-forming reaction was carried out using different concentrations of the monomeric building block and different reaction times. As a result, branched polyphenylenes with M w in the range of 1.2 × 104−12 × 104 g mol-1 were obtained. Both the model compound and the polymers were subjected to intramolecular oxidative cyclodehydrogenation with copper(II) trifluoromethanesulfonate and aluminum chloride. According to LD-TOF mass spectrometry, the cyclodehydrogenation of the model compound afforded the planarized polycyclic aromatic hydrocarbon C66H26. This polycyclic aromatic compound was isolated in 91% yield. The extended π-conjugation and ordering of cyclodehydrogenated products were demonstrated by Raman spectroscopy.

Biomass processing to value-added chemicals and biofuels received considerable attention due to the renewable nature of the precursors. Here, we report the development of Ru-containing magnetically recoverable catalysts for cellulose hydrogenolysis to low alcohols, ethylene glycol (EG) and propylene glycol (PG). The catalysts are synthesized by incorporation of magnetite nanoparticles (NPs) in mesoporous silica pores followed by formation of 2 nm Ru NPs. The latter are obtained by thermal decomposition of ruthenium acetylacetonate in the pores. The catalysts showed excellent activities and selectivities at 100% cellulose conversion, exceeding those for the commercial Ru/C. High selectivities as well as activities are attributed to the influence of Fe3O4 on the Ru(0)/Ru(4+) NPs. A facile synthetic protocol, easy magnetic separation, and stability of the catalyst performance after magnetic recovery make these catalysts promising for industrial applications.

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Here we developed a new family of Zn-containing magnetic oxides of different structures by thermal decomposition of Zn(acac)2 in the reaction solution of preformed magnetite nanoparticles (NPs) stabilized by polyphenylquinoxaline. Upon an increase of the Zn(acac)2 loading from 0.15 to 0.40 mmol (vs 1 mmol of Fe(acac)3), the Zn content increases, and the Zn-containing magnetic oxide NPs preserve a spinel structure of magnetite and an initial, predominantly multicore NP morphology. X-ray photoelectron spectroscopy (XPS) of these samples revealed that the surface of iron oxide NPs is enriched with Zn, although Zn species were also found deep under the iron oxide NP surface. For all the samples, XPS also demonstrates the atom ratio of Fe(3+)/Fe(2+) = 2:1, perfectly matching Fe3O4, but not ZnFe2O4, where Fe(2+) ions are replaced with Zn(2+). The combination of XPS with other physicochemical methods allowed us to propose that ZnO forms an ultrathin amorphous layer on the surface of iron oxide NPs and also diffuses inside the magnetite crystals. At higher Zn(acac)2 loading, cubic ZnO nanocrystals coexist with magnetite NPs, indicating a homogeneous nucleation of the former. The catalytic testing in syngas conversion to methanol demonstrated outstanding catalytic properties of Zn-containing magnetic oxides, whose activities are dependent on the Zn loading. Repeat experiments carried out with the best catalyst after magnetic separation showed remarkable catalyst stability even after five consecutive catalytic runs.

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