Alkaline Ionic Liquids Immobilized on Protective Copolymers Coated Magnetic Nanoparticles: An Efficient and Magnetically Recyclable Catalyst for Knoevenagel Condensation

Magnetite Nanoparticles Functionalized with Thermoresponsive Polymers as a Palladium Support for Olefin and Nitroarene Hydrogenation

A thermoresponsive and recyclable nanomaterial was synthesized by surface modification of magnetite nanoparticles (MNPs) with poly(N-isopropylacrylamide-co-diethylaminoethyl methacrylate) (P(NIPAAm-co-DEAEMA)), having PNIPAAm as a thermoresponsive moiety and PDEAEMA for catalyst binding. Palladium (Pd) nanoparticles were incorporated into this material, and the resulting nanocatalyst was efficient in the hydrogenation of olefins and nitro compounds with turnover frequencies (TOFs) up to 750 h^-1. Consistent catalytic activity in 10 consecutive runs was observed when performing the hydrogenation at 45 °C, i.e., above the lower critical solution temperature (LCST) of the copolymer (37 °C), followed by cooling to 15 °C, i.e., below the LCST of the copolymer.

Assessment of Performance of Photocatalytic Nanostructured Materials with Varied Morphology Based on Reaction Conditions

Synthesis of nanomaterials with specific morphology is an essential aspect for the optimisation of its properties and applications. The application of nanomaterials is being discussed in a wide range of areas, one of which is directly relevant to the environment through photocatalysis. To produce an effective photocatalyst for environmental applications, morphology plays an important role as it affects the surface area, interfaces, crystal facets and active sites, which ultimately affects efficiency. The method of synthesis and synthesis temperature can be the basic considerations for the evaluation of a particular nanomaterial. In this study, we have considered the aspects of morphology with a basic understanding and analyzed them in terms of nanomaterial efficacy in photocatalysis. Different morphologies of specific nanomaterials such as titanium dioxide, zinc oxide, silver phosphate, cadmium sulphide and zinc titanate have been discussed to come to reasonable conclusions. Morphologies such as nanorods, nanoflower, nanospindles, nanosheets, nanospheres and nanoparticles were compared within and outside the domain of given nanomaterials. The different synthesis strategies adopted for a specific morphology have been compared with the photocatalytic performance. It has been observed that nanomaterials with similar band gaps show different performances, which can be linked with the reaction conditions and their nanomorphology as well. Materials with similar morphological structures show different photocatalytic performances. TiO₂ nanorods appear to have the best features of efficient photocatalyst, while the nanoflowers show very low efficiency. For CdS, the nanoflower is the best morphology for photocatalysis. It appears that high surface area is the key apart from the morphology, which controls the efficiency. The overall understanding by analyzing all the available information has enumerated a path to select an effective photocatalyst amongst the several nanomaterials available. Such an analysis and comparison is unique and has provided a handle to select the effective morphology of nanomaterials for photocatalytic applications.

Polyphosphazene-Functionalized Microspheres as Efficient Catalysts for the Knoevenagel Reaction under Mild Conditions

Inspired by the formation of microspheres by hexachlorocyclotriphosphazene and 4, 4'-sulfonyldiphenol, polyphosphazene-functionalized microspheres were developed. Benefits from the supported supper basic phosphazene, the yield exceeded 99 % at room temperature in the manner of second-order reaction kinetics toward Knoevenagel reaction and was still maintained at 99 % after 16 runs. In the experimental temperature from 0 °C to 90 °C, the yield increased from 92 % to 99 %, reflecting that the catalyst had strong applicability under mild conditions. This behavior was conducive to energy conservation. Meanwhile, simple separation and recovery further enhanced this advantage. In addition, the catalyst was also found to be insensitive to aqueous solution or organic solvents such as toluene, THF, EtOH and CH₃ CN. This property gave the Knoevenagel reaction a vast choice. All these features exhibit that this novel catalyst is an attractive and applicable alternative in organic synthesis.

MNP-cellulose-OSO3H as an efficient and biodegradable heterogeneous catalyst for green synthesis of trisubstituted imidazoles

Cellulose is an eco-friendly, efficient, and suitable substrate for use as a coating material and support in the preparation of catalysts. Herein, MNP–cellulose–OSO₃H was prepared as an efficient heterogeneous catalyst composed of Fe₃O₄ nanoparticles covered with cellulose–OSO₃H and used for the synthesis of trisubstituted imidazoles. The catalyst was characterized by FT-IR, CHNS, ICP, PXRD, EDAX, elemental mapping, SEM, TEM, zeta potential, TGA, and VSM techniques. The catalytic activity was evaluated in the one-pot three-component synthesis of trisubstituted imidazole derivatives using benzil or 9,10-phenanthrenequinone, different aldehydes, and ammonium acetate in EtOH solvent at 80 °C over 30 min. The yields of products were excellent, in the range 83–97%. The catalyst showed outstanding catalytic performance toward heating conditions and good reusability. Also, this methodology had several advantages, such as simple procedures, short reaction time, excellent yield, simple workup, and mild reaction conditions.

Cellulose is an eco-friendly, efficient, and suitable substrate for use as a coating material and support in the preparation of catalysts.

Nanocage-based {In2Tm2}-organic framework for efficiently catalyzing the cycloaddition reaction of CO2 with epoxides and Knoevenagel condensation

The combination of [In2Tm2(μ2-OH)2(CO2)10(H2O)2] clusters and H5BDCP ligand generated a highly robust nanoporous MOF with high catalytic performance in the cycloaddition reaction of epoxides with CO2 and Knoevenagel condensation.

Pomegranate-like Core-Shell Ni-NSs@MSNSs as a High Activity, Good Stability, Rapid Magnetic Separation, and Multiple Recyclability Nanocatalyst for DCPD Hydrogenation

A novel pomegranate-like Ni-NSs@MSNSs nanocatalyst was successfully synthesized via a modified Stöber method, and its application in the hydrogenation of dicyclopentadiene (DCPD) was firstly reported. The Ni-NSs@MSNSs possessed a high specific area (658 m²/g) and mesoporous structure (1.7-3.3 nm). The reaction of hydrogenation of DCPD to endo-tetrahydrodicyclopentadiene (endo-THDCPD) was used to evaluate the catalytic performance of the prepared materials. The distinctive pomegranate-like Ni-NSs@MSNSs core-shell nanocomposite exhibited superior catalytic activity (TOF = 106.0 h^-1 and STY = 112.7 g·L^-1·h^-1) and selectivity (98.9%) than conventional Ni-based catalysts (experimental conditions: Ni/DCPD/cyclohexane = 1/100/1000 (w/w), 150 °C, and 2.5 MPa). Moreover, the Ni-NSs@MSNSs nanocatalyst could be rapidly and conveniently recycled by magnetic separation without appreciable loss. The Ni-NSs@MSNSs also exhibited excellent thermal stability (≥750 °C) and good recycling performance (without an activity and selectivity decrease in four runs). The superior application performance of the Ni-NSs@MSNSs nanocatalyst was mainly owing to its unique pomegranate-like structure and core-shell synergistic confinement effect.

Recovery/Reuse of Heterogeneous Supported Spent Catalysts

The rapid separation and efficient recycling of catalysts after a catalytic reaction are considered important requirements along with the high catalytic performances. In this view, although heterogeneous catalysis is generally less efficient if compared to the homogeneous type, it is generally preferred since it benefits from the easy recovery of the catalyst. Recycling of heterogeneous catalysts using traditional methods of separation such as extraction, filtration, vacuum distillation, or centrifugation is tedious and time-consuming. They are uneconomic processes and, hence, they cannot be carried out in the industrial scale. For these limitations, today, the research is devoted to the development of new methods that allow a good separation and recycling of catalysts. The separation process should follow a procedure economically and technically feasible with a minimal loss of the solid catalyst. The aim of this work is to provide an overview about the current trends in the methods of separation/recycling used in the heterogeneous catalysis.

Structural Regulation of Magnetic Polymer Microsphere@Ionic Liquids with an Intermediate Protective Layer and Application as Core-Shell-Shell Catalysts with High Stability and Activity

A novel ionic liquid immobilized on a magnetic polymer microsphere catalyst is reported in this paper. The obtained core-shell-shell catalyst consisted of magnetic nanoparticles (MNPs) as the core, catalytic inert St-co-DVB as the intermediate protective layer, and cross-linked polyaryl imidazole ionic liquids as the active catalytic layer located at the outermost [Im[OH]/MNPs@P(St-DVB)@P(VBC-DVB)]. This catalyst exhibited a high ion-exchange rate (64.65%), high saturation magnetic strength, and excellent acid and alkali corrosion resistance. In the catalyzed Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate, the conversion of benzaldehyde maintained at 92.1% during six times reuse. Optimizing the materials of the protective layer and regulating the thickness of the inert protective layer decreased the corrosion ratio of MNPs in acidic media from 44.82 to 0.44%. Adjusting the thickness of the catalytic layer realized excellent catalytic activity (97%) and high magnetic response performance. In summary, introducing an inert protective layer to the structure of ionic liquids immobilized on the magnetic polymer microsphere catalyst, regulating its thickness, and optimizing its structure achieved a catalyst with high activity, excellent stability, and easy magnetic separation.