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Relevant academic research and scientific papers

Immobilized Cu(ii) and Co(ii) salen complexes on graphene oxide and their catalytic activity for aerobic epoxidation of styrene

Novel graphene oxide (GO) tethered Cu(ii) and Co(ii) salen complexes [M-Salen-GO (M = Cu, Co)] were synthesized via a stepwise procedure and examined as catalysts in the epoxidation of styrene. Acetonitrile was used as a solvent and air as the oxidant in combination with a sacrificial co-reductant isobutyraldehyde. A comparison with homogeneous salen complexes of Co and Cu and graphene oxide (GO) tethered salen complexes was made. Heterogeneous copper(ii) and cobalt(ii) catalysts were confirmed by X-ray diffraction (XRD), FT-IR, diffusion reflection UV-visible spectroscopy, inductively coupled plasma atomic emission spectroscopy (ICP-AES), TEM, TG, Raman and XPS. FT-IR, diffusion reflection UV-visible and inductively coupled plasma atomic emission spectroscopy (ICP-AES), along with TG, Raman and XPS results showed that Cu(ii) and Co(ii) salen complexes were successfully grafted on GO; X-ray diffraction (XRD) and TEM indicated that the sample structures were well preserved. It was found that heterogeneous catalysts were active and showed good recoverability without significant loss in activity and selectivity within successive runs.

Enhanced aerobic epoxidation of styrene with copper(II), cobalt(II), iron(III), or oxovanadium(IV) salen complexes immobilized onto carbon-coated Fe3O4 nanoparticles hybridized with graphene sheets

Core-shell structural magnetic nanocatalysts, involving carbon-coated magnetic Fe3O4 nanoparticles supported on graphene oxide sheets (mildly reduced graphene oxide (MRGO)/Fe3O4@C) and carbonaceous coatings on magnetic Fe3O4 nanoparticles (Fe3O4@C), for immobilizing metal (CuII, CoII, FeIII or VOIV)-salen complexes were prepared by a facile, green, and efficient chemical approach and first applied in the aerobic epoxidation of styrene with air as the oxidizing agent. The prepared catalysts were characterized by different techniques, such as XRD, TEM, FTIR spectroscopy, inductively coupled plasma atomic emission spectroscopy, TEM, thermogravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. The magnetic nanocatalysts MRGO/Fe3O 4@C-salen-M (M=Cu, Co, Fe, or V) exhibited higher catalytic reactivity than that of the corresponding Fe3O4@C-salen-M (M=Cu, Co, Fe, or V) species possibly owing to site isolation, good dispersion of magnetic Fe3O4 nanoparticles, and an efficiently synergistic effect between the metal complexes and the supports. Furthermore, MRGO/Fe3O4@C-salen-Co exhibited up to 92.3% conversion of styrene and 59.2% selectivity to the styrene oxide upon using air as the oxidizing agent and showed good recoverability with negligible loss in activity and selectivity within successive runs owing to superparamagnetism. Most importantly, these materials can be easily recovered by simple magnetic separation. Extra support: Core-shell-structured magnetic nanocatalysts have been prepared and used as efficient heterogeneous catalysts for the aerobic oxidation of styrene. Mildly reduced graphene oxide (MRGO; see picture)/Fe 3O4@C-salen-Co showed over 91% conversion of styrene and over 52% selectivity to the styrene oxide. The materials can be easily recovered through simple magnetic separation. Copyright

Dioxomolybdenum(VI) complex covalently attached to amino-modified graphene oxide: Heterogeneous catalyst for the epoxidation of alkenes

Transition metal salen complex MoO2-salen was successfully tethered onto amino-functionalized graphene oxide (designated as MoO 2-salen-GO), which was tested in the epoxidation of various alkenes using tert-butylhydroperoxide or H2O2 as oxidant. Characterization results showed that dioxomolybdenum(VI) complex was successfully grafted onto the amino-functionalized graphene oxide and the structure of the graphene oxide was well preserved after several stepwise synthesis procedures. Catalytic tests showed that heterogeneous catalyst MoO2-salen-GO was more active than its homogeneous analogue MoO 2-salen in the epoxidation of cyclooctene due to site isolation. In addition, the MoO2-salen-GO catalyst could be reused three times without significant loss of activity.

Oxovanadium(iv) and iron(iii) salen complexes immobilized on amino-functionalized graphene oxide for the aerobic epoxidation of styrene

Oxovanadium(iv) and iron(iii) salen complexes grafted onto amino-modified graphene oxide (NH2-GO) have been synthesized via a stepwise procedure and the prepared materials were used as heterogeneous catalysts in the aerobic oxidation of styrene. The structures of these materials have been thoroughly investigated using different characterization techniques such as XRD, N2 adsorption-desorption, TEM, FT-IR, diffuse reflectance UV-visible spectroscopy, ICP-AES, TEM, TG, Raman, and XPS. The results of XRD, N 2 adsorption-desorption and TEM revealed that the structures of the prepared catalysts were well preserved. In addition, the results of FT-IR, diffuse reflectance UV-visible spectroscopy, ICP-AES, TG, Raman and XPS suggested that the oxovanadium(iv) and iron(iii) complexes had been incorporated onto amino-modified graphene oxide (GO). It was found that the heterogeneous oxovanadium(iv) catalyst was more active than its homogeneous analogue in the epoxidation of styrene, using acetonitrile as solvent and air as the oxidant in combination with the sacrificial co-reductant isobutyraldehyde, due to site-isolation. Furthermore, the tethered vanadium catalyst was quite stable and could be recycled many times.

Heterogenization of functionalized Cu(II) and VO(IV) Schiff base complexes by direct immobilization onto amino-modified SBA-15: Styrene oxidation catalysts with enhanced reactivity

Two functionalized copper(II) and oxovanadium(IV) Schiff base complexes of type [M(N2O2), M = Cu, VO] bearing chloromethyl groups were respectively synthesized, directly anchored onto amino-modified SBA-15 materials and examined as catalysts for styrene oxidation. The purity of each ligand was confirmed by 1H NMR, FT-IR and elemental analysis. XRD, N2 adsorption/desorption and TEM results indicated that the mesoporous structure of SBA-15 remained intact throughout the grafting procedure. FT-IR, UV-vis spectroscopy plus TG-DTA data demonstrated the incorporation of copper(II) and oxovanadium(IV) complexes on amino-modified SBA-15. ICP-AES, SEM-EDX combined with XPS data further showed the different anchorage status of copper(II) and oxovanadium(IV) species on amino-modified SBA-15. The copper(II) Schiff base complex was anchored through the coordination of copper atom with the nitrogen atom of the amino group modified on the SBA-15 external surface. The oxovanadium(IV) Schiff base complex, however, was covalently anchored on SBA-15 via the condensation reaction of the chloromethyl group of the Schiff base with the amino group from the modified SBA-15 matrix. The catalytic properties of supported copper(II) and oxovanadium(IV) complexes in the oxidation of styrene with air or H2O2 as oxidant were investigated and compared with the properties of their homogeneous analogues. It was found that both heterogeneous copper(II) and oxovanadium(IV) catalysts were more active than their homogeneous analogues and that the product selectivity varied in cases of different oxidants. The supported oxovanadium(IV) complex showed high yield of styrene oxide (56.0%) and good recoverability when using air as oxidant.