Effect of preparation parameters on characterization and activity of Co3O4 catalyst in liquid phase oxidation of lignin model substrates

• The nano Co3O4 spinel prepared by co-precipitation.
• Excellent activity achieved for liquid phase oxidation of lignin sub-structure compounds: veratryl alcohol, vanillyl alcohol, sinapyl alcohol, coniferyl alcohol.
• Catalyst activity was a function of its morphology depending on pH, calcination temperature and time.
• Co3O4 showed the stoichiometric distribution of octahedral Co3+ and tetrahedral Co2+ species, responsible for its highest redox ability.

The nano structured spinel cobalt oxide (Co3O4) was prepared via simple co-precipitation method and its catalytic activity was evaluated for the liquid phase aerobic oxidation of lignin sub structure compounds such as veratryl alcohol. Catalyst preparation parameters influenced its morphology eventually affecting its oxidation activity. Thus, nano rod shaped Co3O4 catalyst showed 75% and 38% conversion of veratryl alcohol with complete selectivity to veratryl aldehyde in toluene and water, respectively, under base free condition. The influence of reaction conditions, such as temperature, oxygen pressure and catalyst loading was studied to obtain the optimum product yield and selectivity to the desired product. Furthermore, oxidation of various sub-structures of lignin model compounds was also studied over the same catalyst which was found to be in the following order: secondary alcohol > di-substituted > tri-substituted > mono-substituted > non-substitution. The stability of the catalyst was confirmed by its successful recycle for three times.

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