Preparation of magnetic nanocomposites of solid acid catalysts and their applicability in esterification

NB. Highly efficient CdS/CeO2/Ag3PO4 nanocomposite as novel heterogenous catalyst for Knoevenagel condensation and acetylation reactions

In light of environmental and economic concerns, the use of heterogeneous catalysts that can function under gentler reaction conditions has recently become popular. In this study by using the precipitation method, CdS/CeO2/Ag3PO4 ternary nanocomposites with varied molar proportions of CdS:CeO2/Ag3PO4 were produced. The catalysts' surface functional groups; morphology and crystal structures were examined using FTIR, SEM-EDX and XRD respectively. The catalytic efficiency of all synthesized nanomaterials was tested on a model Knoevenagel condensation reaction. For the best catalyst, selected from the screening, the optimization of reaction conditions such as the solvent, catalyst load, concentration of reagents such as malononitrile/acetic anhydride, and temperature. The ternary nanocomposite CdS/CeO2/Ag3PO4 (4:1) displayed higher catalytic activity (95.4 ± 3.2 %) than the rest of the nanomaterials prepared. Thus, the ternary nanocomposite CdS/CeO2/Ag3PO4 with 4:1 mol ratio with optimized reaction conditions was used to check the substrate scope of Knoevenagel condensation and acetylation reaction. The synthesized Knoevenagel condensation and acetylation reaction products were also characterized by proton and carbon NMR for their structure determination. The nanocomposite's reusability was carried out and only 7.5 ± 2 % decrement was witnessed after four runs and 23.3 % after the fifth run. and this indicates the potential application of the catalyst to organic reactions. Furthermore, we have proposed the possible catalytic mechanisms for both organic reactions.

Magnetic-responsive solid acid catalysts for esterification

Two kinds of magnetic-responsive solid acid catalysts were designed and prepared via an in situ polymerization of poly(ionic liquid)s (PILs) on the surface of Fe3O4@SiO2 NPs for the catalyzed esterification of palmitic acid and methanol. They were characterized using XRD, TGA, VSM, NMR spectroscopy, FTIR spectroscopy, XPS, SEM, and GC techniques. The results confirmed the preparation of solid acid catalysts. Meanwhile, they possessed excellent catalytic activity and recyclability. The effect of the reaction conditions on the esterification was investigated through single-factor analyses, and the proposed catalytic mechanism of the prepared solid acid catalysts in the esterification are also discussed. Under the optimal reaction conditions (10 wt% catalyst, 6 h, 70 °C, and molar ratio (MR) of methanol to palmitic acid of 12 : 1), the conversion rate of palmitic acid could reach 94% and 79% with Fe3O4@SiO2-poly(1-vinyl-3-ethylimidazolium phosphotungstate) (Fe3O4@SiO2-P([VLIM]PW)) and Fe3O4@SiO2-poly(1-vinylimidazole-3-propyl sulfonate) (Fe3O4@SiO2-P([VLIM]SO3)) NPs serving as catalysts, respectively. Furthermore, the Fe3O4@SiO2-P([VLIM]PW) NPs could still maintain a high catalytic activity even after being reused 5 times without significant deactivation.

Preparation and Characterization of Sulfonated Magnetic SiO2 Microspheres as the Solid Acid Catalysts for Esterification

The sulfonated magnetic SiO₂ microsphere solid acid catalysts were prepared by the impregnation and grafting methods with iron oxide magnetic nanoparticles (Fe₃O₄ MNPs) as the magnetic cores. The catalytic properties of the magnetic SiO₂ solid acid catalyst were studied in detail. The characterization results showed that the SiO₂ was successfully coated on the Fe₃O₄ MNPs. Compared with the grafting method, impregnated solid acid exhibits higher catalytic performance, which reached an esterification rate of up to 99.00% when the reaction temperature was 105 °C, the molar ratio of n-butanol/adipic acid was 3:1, and the ratio of the catalyst (the mass of magnetic solid acid) to liquids (the total volume of n-butanol and adipic acid) was 2.95%. The magnetic solid acid exhibited great separation ability and reusability. After six times of recycle, the conversion of the grafted magnetic solid acid still attained 85.61% compared with that of the impregnated magnetic solid acid, which reduced to 81.35%, holding great potential for green chemical processes.

Fe3O4@SiO2 supported aza-crown ether complex cation ionic liquids: preparation and applications in organic reactions

A series of aza-crown ether ionic liquids supported on magnetic Fe₃O₄@SiO₂ core–shell particles were designed, synthesized and characterized by elemental analysis, TEM, TG and FT-IR.