Magnetically Separable Base Catalysts: Heterogeneous Catalysis vs. Quasi-Homogeneous Catalysis

The synthesis of magnetically separable quasi-homogeneous base catalyst and heterogeneous base catalyst is described. The quasi-homogeneous catalyst is achieved by supporting silane monomers functionalized with different amine groups directly on the surface of magnetite nanoparticles. The heterogeneous catalyst is prepared via a sol-gel process in which silane monomers containing different amine groups are copolymerized with tetraethoxysilane in the presence of magnetite nanoparticles functionalized with ionic liquid moieties. The reactivity of the quasi-homogeneous and the heterogeneous base catalysts is compared in the nitroaldol condensation

Highly Active Ruthenium Catalyst Supported on Magnetically Separable Mesoporous Organosilica Nanoparticles

A facile and direct method for synthesizing magnetic periodic mesoporous organosilica nanoparticles from pure organosilane precursors is described. Magnetic ethylene- and phenylene-bridged periodic mesoporous organosilica nanoparticles (PMO NPs) were prepared by nanoemulsification techniques. For fabricating magnetic ethylene- or phenylene-bridged PMO NPs, hydrophobic magnetic nanoparticles in an oil-in-water (o/w) emulsion were prepared, followed by a sol–gel condensation of the incorporated bridged organosilane precursor (1,2 bis(triethoxysilyl)ethane or 1,4 bis(triethoxysilyl)benzene), respectively. The resulting materials were characterized using high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray (EDX) spectroscopy, powder X-ray diffraction (XRD), solid-state NMR analysis, and nitrogen sorption analysis (N2-BET). The magnetic ethylene-bridged PMO NPs were successfully loaded using a ruthenium oxide catalyst by means of sonication and evaporation under mild conditions. The obtained catalytic system, termed Ru@M-Ethylene-PMO NPS, was applied in a reduction reaction of aromatic compounds. It exhibited very high catalytic behavior with easy separation from the reaction medium by applying an external magnetic field

Preparation of Poly(ethylene glycol)@Polyurea Microcapsules Using Oil/Oil Emulsions and Their Application as Microreactors

The development process of catalytic core/shell microreactors, possessing a poly(ethylene glycol) (PEG) core and a polyurea (PU) shell, by implementing an emulsion-templated non-aqueous encapsulation method, is presented. The microreactors’ fabrication process begins with an emulsification process utilizing an oil-in-oil (o/o) emulsion of PEG-in-heptane, stabilized by a polymeric surfactant. Next, a reaction between a poly(ethylene imine) (PEI) and a toluene-2,4-diisocyanate (TDI) takes place at the boundary of the emulsion droplets, resulting in the creation of a PU shell through an interfacial polymerization (IFP) process. The microreactors were loaded with palladium nanoparticles (NPs) and were utilized for the hydrogenation of alkenes and alkynes. Importantly, it was found that PEG has a positive effect on the catalytic performance of the developed microreactors. Interestingly, besides being an efficient green reaction medium, PEG plays two crucial roles: first, it reduces the palladium ions to palladium NPs; thus, it avoids the unnecessary use of additional reducing agents. Second, it stabilizes the palladium NPs and prevents their aggregation, allowing the formation of highly reactive palladium NPs. Strikingly, in one sense, the suggested system affords highly reactive semi-homogeneous catalysis, whereas in another sense, it enables the facile, rapid, and inexpensive recovery of the catalytic microreactor by simple centrifugation. The durable microreactors exhibit excellent activity and were recycled nine times without any loss in their reactivity

Magnetic Polyurea Nano-Capsules Synthesized via Interfacial Polymerization in Inverse Nano-Emulsion

Polyurea (PU) nano-capsules have received voluminous interest in various fields due to their biocompatibility, high mechanical properties, and surface functionality. By incorporating magnetic nanoparticle (MNPs) into the polyurea system, the attributes of both PU and MNPs can be combined. In this work, we describe a facile and quick method for preparing magnetic polyurea nano-capsules. Encapsulation of ionic liquid-modified magnetite nanoparticles (MNPs), with polyurea nano-capsules (PU NCs) having an average size of 5–20 nm was carried out through interfacial polycondensation between amine and isocyanate monomers in inverse nano-emulsion (water-in-oil). The desired magnetic PU NCs were obtained utilizing toluene and triple-distilled water as continuous and dispersed phases respectively, polymeric non-ionic surfactant cetyl polyethyleneglycol/polypropyleneglycol-10/1 dimethicone (ABIL EM 90), diethylenetriamine, ethylenediamine diphenylmethane-4,4′-diisocyanate, and various percentages of the ionic liquid-modified MNPs. High loading of the ionic liquid-modified MNPs up to 11 wt% with respect to the dispersed aqueous phase was encapsulated. The magnetic PU NCs were probed using various analytical instruments including electron microscopy, infrared spectroscopy, X-ray diffraction, and nuclear magnetic spectroscopy. This unequivocally manifested the successful synthesis of core-shell polyurea nano-capsules even without utilizing osmotic pressure agents, and confirmed the presence of high loading of MNPs in the core

Palladium Nanoparticles Supported on Magnetic Organic-Silica Hybrid Nanoparticles

A method for supporting palladium nanoparticles on magnetically separable organosilica nanoparticles functionalized with ionic liquid groups is described. The system was prepared by sol–gel condensation of two silica precursors: tetraethyl orthosilicate (TEOS) and bis-silylated ionic liquid monomer, on hydrophobic magnetic nanoparticles modified with oleate groups. The support of palladium nanoparticles on the magnetic organo-silica hybrid nanoparticles was achieved by adsorbing palladium salts (Na₂PdCl₄) on their surface via ion exchange with the ionic liquid groups, followed by reduction with sodium borohydride. The resulted system was applied in three different catalytic transformations: carbonylation of iodoarenes and Heck and Suzuki coupling reactions. The catalyst demonstrated high catalytic activity and was easily separated from the reaction mixture by applying an external magnetic field. The catalyst was recycled over five times without showing a significant loss in its activity

High-Complexity WO3-Based Catalyst with Multi-Catalytic Species via 3D Printing

Three-dimensional (3D) printing has recently been introduced into the field of chemistry as an enabling tool employed to perform reactions, but so far, its use has been limited due to material and structural constraints. We have developed a new approach for fabricating 3D catalysts with high-complexity features for chemical reactions via digital light processing printing (DLP). PtO2-WO3 heterogeneous catalysts with complex shapes were directly fabricated from a clear solution, composed of photo-curable organic monomers, photoinitiators, and metallic salts. The 3D-printed catalysts were tested for the hydrogenation of alkynes and nitrobenzene, and displayed excellent reactivity in these catalytic transformations. Furthermore, to demonstrate the versatility of this approach and prove the concept of multifunctional reactors, a tungsten oxide-based tube consisting of three orderly sections containing platinum, rhodium, and palladium was 3D printed

Platinum nanoparticles supported on ionic liquid-modified magnetic nanoparticles : Selective hydrogenation catalysts

A method for supporting platinum nanoparticles on magnetite nanoparticles is described. The method requires modification of the surface of the magnetic nanoparticles with ionic liquid groups. Before modification, the magnetic nanoparticles are not stable and easilyaggrega te and, after modification, the magnetite nanoparticles become highly stable and soluble in polar or non-polar organic solvents depending on the alkyl group of the linked ionic liquids. The supporting of platinum nanoparticles on the modified magnetic nanoparticles was achieved byadsorb ing platinum salts (K\u2082PtCl\u2084) on the surface of the magnetite nanoparticles via ion exchange with the linked ionic liquid groups and then reducing them byhy drazine. The supported platinum nanoparticles were applied in the catalytic hydrogenation of alkynes in which cis-alkenes were selectivelyproduce d, and in the hydrogenation of \u3b1,\u3b2-unsaturated aldehydes where the allyl alcohols were obtained as the exclusive products. The new catalyst can be easilysep arated from the reaction mixtures by applying an external magnetic field and recycled.Peer reviewed: YesNRC publication: Ye

Metal supported on dendronized magnetic nanoparticles: highly selective hydroformulation catalysts

A method for homogenizing heterogeneous catalyst is described. The method is based on growing polyaminoamido (PAMAM) dendrons on silica-coated magnetic nanoparticles. After the dendronizing process, the silica-coated magnetic nanoparticles are more stable and more soluble in organic solvents. The dendronized particles are phosphonated, complexed with [Rh(COD)Cl]2, and applied in catalytic hydroformylation reactions. These new catalysts are proven to be highly selective and reactive.Peer reviewed: YesNRC publication: Ye

BMIm-PF₆@SiO₂ Microcapsules: Particulated Ionic Liquid as A New Material for the Heterogenization of Catalysts

A method for the preparation of silica microcapsules containing a high loading of ionic liquids (ILs) is described. The method paves the way to the conversion of ionic liquids into particulated materials, which results in ILs with new properties without changing their molecular structures. The synthesis of these new materials is based on the emulsification of ionic liquids in water, using surfactants or dispersants, and the resulting ionic liquid droplets are then confined in a silica shell formed via interfacial hydrolysis and polycondensation of tetraethoxysilane. This material can be isolated by centrifugation, followed by drying to yield a fine powder of ionic liquid-silica microcapsules, which are water and organic solvents redispersible. These new materials are utilized in the heterogenization of palladium catalyst and then applied in the hydrogenation of alkynes. The catalyst shows chemoselectivity in the hydrogenation of internal alkynes such as 4-octyne. Comparative studies have shown that the same catalyst loses this selectivity when it is applied under homogeneous conditions