Sol–gel derived mesoporous cobalt silica catalyst: Synthesis, characterization and its activity in the oxidation of phenol

Abstract

• Heterogeneous cobalt catalysts were synthesized from agricultural biomass. • Cobalt catalysts were highly dispersed and exhibited good textural properties. • The catalysts were active in the oxidation of phenol at ambient condition. • The catalysis of cobalt catalysts was truly driven by its heterogeneous nature. • RH-10Co was stable even after five consecutive catalytic runs. Highly mesoporous cobalt silica rice husk catalysts with (5–15 wt.%) Co 2+ loading were prepared via a simple sol–gel technique at room temperature. The successful insertion of cobalt ions into silica matrix was evidenced from FT-IR, NMR, XPS and AAS analyses. Preservation of the mesoporosity nature of silica upon incorporating Co 2+ was confirmed from the N 2 -sorption studies. The topography and morphology viewed by TEM analysis differs as the cobalt concentration varies from 5 to 15 wt.%. Parallel pore channels and spherical nanoparticles of 9.44 nm were achieved for cobalt silica catalysts with 10 and 15 wt.% respectively. Cobalt catalysts were active in the liquid-phase oxidation of phenol with H 2 O 2 as an oxygen source. The performances of the catalysts were greatly influenced by various parameters such as reaction temperature, catalyst amount, molar ratio of substrate to oxidant, nature of solvent, metal loading and homogeneous precursor salt. Water served as the best reaction medium for this oxidation system. The regeneration studies confirmed cobalt catalyst could be reused for five cycles without experiencing large loss in the conversion. Both leaching and reusability studies testified that the catalysts were truly heterogeneous.