SBA-15 supported cobalt oxide species: Synthesis, morphology and catalytic oxidation of cyclohexanol using TBHP

• A blue powder forms when SBA-15 is loaded with various amount of CoCl2·6H2O.
• The color intensity of the Co-composites is proportional to the Co-loading.
• Cobalt oxide species are highly dispersed throughout the SBA-15 after calcination.
• The dominant phase in all Co-composites is Co2+ in tetrahedral co-ordination.
• Calcination results in a morphological transformation in Co-composites with ≥30 wt% Co.

SBA-15 type silica was loaded with CoCl2·6H2O via using the two-solvent, impregnation and adsorption methods, then calcined to prepare a range of supported composites with varying Co-loadings. Each of the products had a blue color with intensity proportional to the Co-loading. DR UV–vis and XPS results demonstrate the presence of Co2+ in tetrahedral co-ordination. A wide variety of methods were used to characterize the Co-composites. An unexpected morphological transformation was observed in composites prepared with Co-loadings of 30 wt% or more, such that the original SBA-15 channels were no longer present. Nevertheless, all the composite materials exhibited high activity in catalyzing the liquid phase oxidation of cyclohexanol using tert-butylhydroperoxide (TBHP) as an oxidant. Some leakage of the catalytically active species into the solution was observed, implying that the catalyst is behaving as a mixed heterogeneous–homogeneous system. Thus, the high catalytic activity for these Co-composites can be attributed to high dispersion of the active sites throughout the support and/or the presence of active species in solution.

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