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

Abstract

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/Fe3O4@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.

Recent Advancements in Graphene‐Based Supports of Metal Complexes/Oxides for Epoxidation of Alkenes

“…[16] Similarr esultsw ere achieved for RGO/Fe 3 O 4 @C-salen-MoO 2 in cyclooctene and geraniol epoxidation with tert-butyl hydroperoxide (TBHP)/H 2 O 2 as the oxidants. [16] Similarr esultsw ere achieved for RGO/Fe 3 O 4 @C-salen-MoO 2 in cyclooctene and geraniol epoxidation with tert-butyl hydroperoxide (TBHP)/H 2 O 2 as the oxidants.…”

Oxovanadium catalyst based on nano-porous carbon xerogel: an efficient heterogeneous nano-catalyst for aerobic oxidation of olefins

“…Furthermore, 1-decene is epoxidized slower than 1-octene since larger octyl group connected to double bond sterically hinders it in approaching the catalyst metal center with respect to 1-octene which its double bond carrying a smaller hexyl group [48]. Epoxide selectivity and conversion of CXG/[VO(HL) (H 2 O)(CH 3 OH)] in the oxidation of styrene is higher than the previously reported systems such as VO-GO and VO-salen-GO [49], PS-[VO(ligand) n ] [50], VO-salen-SBA [51], and MRGO/Fe 3 O 4 @C-salen-V [52]. This behavior could be related to the surface chemistry of the carbon material plays a decisive role on its catalytic properties, providing active sites capable of chemisorbing the reactants and forming surface intermediates of adequate strength.…”

Facile fabrication of magnetic MoO2–Salen‐modified graphene‐based catalyst for epoxidation of alkenes

“…RGO/Fe 3 O 4 @C‐Salen was prepared successfully in our previous work . Typically, a mixture of 1.0 g of RGO/Fe 3 O 4 @C‐NH 2 and 1.15 mmol of CM‐SalenH 2 in pre‐dried toluene was refluxed under nitrogen atmosphere for 24 h, magnetically separated, washed with toluene, Soxhlet‐extracted with CH 2 Cl 2 and dried.…”

“…But beyond that, the dye removal efficiency was 86 and 77% after five cycles in water and 1 M HCl, respectively. The immobilization of Cu(II), Co(II), Fe(III) or VO(IV) Salen complexes onto carbon‐coated Fe 3 O 4 nanoparticles hybridized with graphene (RGO/Fe 3 O 4 @C) achieved core@shell structured magnetic nanocatalysts that exhibited high activity for the epoxidation of styrene …”