Facile synthesis of Co-SBA-16 mesoporous molecular sieves with EISA method and their applications for hydroxylation of benzene

Abstract

A series of cobalt-doped SBA-16 (Co-SBA-16) mesoporous molecular sieves with different Co/Si ratio have been directly synthesized by the evaporation induced self-assembly (EISA) method. Characterizations with XRF, XRD, TEM and N2 adsorption–desorption measurements demonstrate that the resultant materials remain a relative ordered cubic cage-like (Im3m) mesostructure wherein a certain amount of cobalt is introduced. Not only the mesostructure of SBA-16, but also the nature and distribution of Co species are strongly affected by the Co/Si ratio in the synthesis of Co-SBA-16. The results of XRD, FT-IR, 29Si MAS NMR, XPS, H2-TPR and DRUV–vis spectra suggest that the introduced cobalt species in Co-SBA-16 mainly exist as isolated Co(II) species in tetrahedral coordination. Most of them are incorporated into silica wall as single framework Co2+ site while other isolated Co(II) species locate on the surface of SBA-16 silica. The excellent catalytic activity has been obtained for the hydroxylation of benzene to phenol due to the presence of these isolated Co(II) species. The highest phenol yield of 28.8% and selectivity of 96.6% with the TON of 51.8 are obtained over Co-SBA-16 catalyst (CS-0.12) using acetic acid as solvent. The reuse and the leaching behavior of cobalt of CS-0.12 catalyst are also investigated.