Catalytic palladium (Pd) nanoparticles on electrospun copolymers of acrylonitrile and acrylic acid (PAN-AA) mats were produced via reduction of PdCl2 with hydrazine. Fiber mats were electrospun from homogeneous solutions of PAN-AA and PdCl2 in dimethylformamide (DMF). Pd cations were reduced to Pd metals when fiber mats were treated in an aqueous hydrazine solution at room temperature. Pd atoms nucleate and form small crystallites whose sizes were estimated from the peak broadening of X-ray diffraction peaks. Two to four crystallites adhere together and form agglomerates. Agglomerate sizes and fiber diameters were determined by scanning and transmission electron microscopy. Spherical Pd nanoparticles were dispersed homogeneously on the electrospun nanofibers. The effects of copolymer composition and amount of PdCl 2 on particle size were investigated. Pd particle size mainly depends on the amount of acrylic acid functional groups and PdCl2 concentration in the spinning solution. Increasing acrylic acid concentration on polymer chains leads to larger Pd nanoparticles. In addition, Pd particle size becomes larger with increasing PdCl 2 concentration in the spinning solution. Hence, it is possible to tune the number density and the size of metal nanoparticles. The catalytic activity of the Pd nanoparticles in electrospun mats was determined by selective hydrogenation of dehydrolinalool (3,7-dimethyloct-6-ene-1-yne-3-ol, DHL) in toluene at 90°C. Electrospun fibers with Pd particles have 4.5 times higher catalytic activity than the current Pd/Al 2O3 catalyst.

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.

Impregnation of hyper-cross-linked polystyrene (HPS) with tetrahydrofuran (THF) or methanol (ML) solutions containing platinic acid results in the formation of Pt(II) complexes within the nanocavities of HPS. Subsequent reduction of the complexes by H2 yields stable Pt nanoparticles with a mean diameter of 1.3 nm in THF and 1.4 nm in ML. The highest selectivity (98% at 100% conversion) measured during the catalytic oxidation of L-sorbose in water is obtained with the HPS-Pt-THF complex prior to H2 reduction. During an induction period of about 100 min, L-sorbose conversion is negligible while catalytic species develop in situ. The structure of the catalyst isolated after the induction period is analyzed by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electron micrographs reveal a broad distribution of Pt nanoparticles, 71% of which measure less than or equal to 2.0 nm in diameter. These nanoparticles are most likely responsible for the high catalytic activity and selectivity observed. The formation of nanoparticles measuring up to 5.9 nm in diameter is attributed to the facilitated intercavity transport and aggregation of smaller nanoparticles in swollen HPS. The catalytic properties of these novel Pt nanoparticles are highly robust, remaining stable even after 15 repeated uses.

The structural transformation and catalytic properties of metal/polymer nanocomposites derived from hypercross-linked polystyrene (HPS) exhibiting both microporosity and macroporosity, and filled with Pt nanoparticles, are investigated in the direct oxidation of L-sorbose to 2-keto-L-gulonic acid. Transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, anomalous small-angle X-ray scattering, and catalytic studies suggest that the catalytically active species, nanoparticles of mixed composition with a mean diameter of 1.6 nm, develop after the initial induction period. At the highest selectivity (96.8%) at 100% L-sorbose conversion, the catalytic activity is measured to be 2.5 × 10-3 mol/mol Pt-s, which corresponds to a 4.6-fold increase in activity relative to the Pt-modified microporous HPS previously reported. This substantial increase in catalytic activity is attributed to the presence of macropores, which facilitate mass transport and, consequently, accessibility of the nanoparticle surface for reactants.