Reconstruction of cobalt magnesium aluminum hydrotalcite loaded ruthenium using the memory effect for selective oxidation of 5-hydroxymethylfurfural under alkali-free conditions

The hydrotalcite CoMgAl-LDH was prepared using a hydrothermal method. The calcined hydrotalcite was rehydrated utilizing its "memory effect", and the catalyst Ru/CoMgAl-RLDH was prepared by loading ruthenium nanoparticles through the impregnation reduction method. The pristine hydrotalcite Co₁Mg₂Al₁-LDH exhibited a specific surface area of 9.2 m² g^-1, while the Ru-loaded reconstructed hydrotalcite Ru₄/Co₁Mg₂Al₁-RLDH demonstrated a significant increase in specific surface area to 130.0 m² g^-1. The total basicity of the original hydrotalcite Co₁Mg₂Al₁-LDH catalyst surface was 0.25 mmol g^-1, and all these basic sites were weak basic sites. By contrast, the total basicity of the reconstructed hydrotalcite Ru₄/Co₁Mg₂Al₁-RLDH catalyst surface was 0.37 mmol g^-1, consisting of weak and moderate basic sites. The reconstructed hydrotalcite not only showed higher thermal stability than the original one but also enabled the systematic adjustment of its basic sites by changing the molar ratio of elements in the hydrotalcite and the calcination temperature. The Ru₄/Co₁Mg₂Al₁-RLDH catalyst prepared with the Co : Mg : Al molar ratio of 1 : 2 : 1, calcination temperature of 400 °C, and Ru loading of 4 wt% demonstrated optimal catalytic activity, achieving complete 5-hydroxymethylfurfural (HMF) conversion and 87.6% 2,5-furandicarboxylic acid (FDCA) yield under alkali-free conditions.