Abstract
Poly(vinylbenzyl chloride-co-divinyl benzene)-based polyHIPE monoliths of different porosities were prepared using high-internal-phase emulsions (HIPEs) containing a fixed amount of vinylbenzyl chloride (VBC, 6.0 g, 0.0393 mol) and divinyl benzene (DVB 4.0 g, 0.0308 mol) as the oil phase and different volume ratios of aqueous calcium chloride as the internal phase. Span-80 (2.0 g (4.67 mmol))-stabilized HIPEs were polymerized at 60 °C using potassium persulfate (0.4 g, 1.48 mmol) as the initiator. Upon varying the volume ratio of aqueous calcium chloride from 80 to 90%, the prepared polyHIPE monoliths have shown significant variations in their surface morphology, specific surface area (SA), and pore volumes (Vp) as confirmed by scanning electron microscopy (SEM) and a gas adsorption (BET) method. The prepared polyHIPE monoliths were anchored with o-hydroxynaphthaldehyde propylenediamine Schiff base ligand (HNPn) and then loaded with copper(ii) ions (HNPn–Cu) to act as a catalyst. The structural information of unsupported HNPn–Cu complexes was obtained by recording its FT-IR and UV-visible spectra. The amount of copper(ii) ions loaded onto HNPn ligand-anchored polyHIPE monoliths was determined by atomic absorption spectroscopic analysis. In comparison to unsupported HNPn–Cu catalyst, the polyHIPE monolith-supported HNPn–Cu catalyst has shown high catalytic activity (66.8%), product selectivity for epoxycyclohexane (ECH) (94.8%), high turn over number (0.028 mol mol−1 h−1) and low energy of activation (22.4 kJ mol−1) in the epoxidation of cyclohexene in the presence of hydrogen peroxide (H2O2) as an oxidant at 40 °C. The polyHIPE-supported HNPn–Cu catalyst also shows high reuse applications. Studies show that there is sufficient scope to develop polyHIPE monoliths with various properties for specific applications.
Highlights
The porous polyHIPE monoliths obtained from high-internalphase emulsions (HIPEs) are able to overcome the channel ow problem usually encountered with polymer gel-beads in continuous ow reactors.[74]
The results indicated that polyHIPE monoliths were able to provide better microenvironment to the reaction intermediate (M–hydroxynaphthaldehyde propylenediamine Schiff base ligand (HNPn)–CH–OOHÀ) for its decomposition to form ECH in comparison to the decomposition of an intermediate on unsupported HNPn–Cu catalyst
The polyHIPE monoliths have been functionalized with o-hydroxy napthaldehyde propylenediamine Schiff base ligands (HNPn) and loaded with copper(II) ions to act as a catalyst (HNPn– Cu) for the epoxidation of cyclohexene in the presence of hydrogen peroxide as an oxidant at 40 C
Summary
Polymer gel-bead, spacers such as polyethylene glycol are used, but cleaving and poor loading of catalyst remained major drawbacks.[3,12,13,14] Some efforts were made to increase the loading capacity of supports by controlling their swelling properties and improving the stability of supported catalysts.[4,15] Property modi cation in polymer gel-bead supports was found to be more useful in continuous ow reactors than batch reactors.[14,16,17,18,19] polymer gel-beads suffered from a channeling effect, which made interior active sites to remain unutilized in ow-through processes.[20] Considering these drawbacks of polymer gel-bead supports, the polyHIPE monoliths without interstitial space[5,6] are found to be more useful and ideal for continuous ow reactors.[19,21,22] To develop porous supports, various techniques such as gas foaming,[23] porogen leaching,[24] and techniques of additive manufacturing[25] are widely used. To improve the properties of polyHIPE monoliths, hyper cross-linking in polyHIPE monoliths was carried out using dimethoxymethane as the external cross-linker.[72,73]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
