Catalytic performance of Cu–Co/metakaolinite: role of textural and structural properties in the partial oxidation of glycerol

Abstract

Cu–Co catalysts were synthesized using microporous and mesoporous metakaolinite and calcined at 400, 600, and 800 °C. The effect of calcination temperature on the textural and structural properties was investigated. Characterization of the solids revealed the formation of a CuCo₂O₄ spinel structure when the catalyst was calcined at 400 °C. Increasing the calcination temperature led to structural modifications in the metallic phase due to the interaction of Cu with Al atoms in the support, which favored the formation of another spinel phase (CuAl₂O₄). Additionally, thermal treatment reduced the specific surface area and pore volume, suggesting an enhanced dispersion of the metal phase. The catalysts were evaluated for their performance in glycerol oxidation, using H₂O₂ as the oxidizing agent in a 0.54 M aqueous glycerol solution at 80 °C under atmospheric pressure. Although all catalysts demonstrated activity, a distinct trend was observed with calcination temperature. The catalyst calcined at 800 °C exhibited the highest activity, achieving complete conversion after 4 hours of reaction and a selectivity of 92% toward dihydroxyacetone. The structural modification of the catalyst at elevated calcination temperatures also resulted in reduced leaching of Cu and Co, indicating improved stability. X-ray Photoelectron Spectroscopy (XPS) analysis revealed a surface enrichment in tetrahedral copper attributed to the formation of the spinel CuAl₂O₄ at high calcination temperature. The beneficial role of copper associated with cobalt was evidenced experimentally and DRIFT analysis indicates that metakaolinite plays a fundamental role in the activation of the secondary OH in glycerol.