Supported cobalt catalysts by one-pot aqueous combustion synthesis for catalytic phenol degradation

Cobalt oxides (Co) and Al2O3-, SiO2-, and TiO2-supported cobalt oxide catalysts were prepared by an aqueous combustion method using urea and glycine as fuels. Their catalytic performance in activation of OXONE® for phenol degradation in aqueous solution was investigated. It was found that unsupported Co oxide and supported Co oxide presented different mechanisms in activation of OXONE® for phenol degradation. The supported Co catalysts presented higher activity in activation of OXONE® for phenol degradation due to higher dispersion of Co3O4 on the supports and Co(II) coordination sites. The major oxidizing radicals were identified to be SO4- by competitive radical reactions. The Co oxides synthesized from urea or glycine showed a similar activity; however, the supported Co catalysts prepared by glycine fuel exhibited better activity than those prepared by urea. For Al2O3-, SiO2-, and TiO2-supported Co catalysts, Co/TiO2 presented a higher activity in phenol degradation compared with Co/SiO2 and Co/Al2O3. But, Co/SiO2 showed the best stability among the catalysts. Total organic carbon could be reduced by 80%, 72%, and 45% on Co/TiO2, Co/SiO2, and Co/Al2O3, respectively, at 30 ppm phenol. Phenol degradation was found to follow the zero-order kinetics. The causes of deactivation were investigated, and the regeneration methods were proposed.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (90 K)Download as PowerPoint slideHighlights► Urea and glycine show effectiveness in synthesis of supported Co oxide catalysts in aqueous solution combustion. ► Supported Co catalysts exhibited higher performance in phenol degradation. ► Activation of OXONE on unsupported and supported Co catalysts was different. ► Co/SiO2 presented higher activity and stability compared with Co/TiO2 and Co/Al2O3. ► Cobalt leaching, intermediate coverage, and surface charge variation induce catalyst deactivation.