Characterization of the active sites in MgNiAl mixed oxides by microcalorimetry and test reaction

In this study, MgNiAl mixed oxides derived from layered double hydroxide precursors were prepared by pH-controlled co-precipitation. Three samples were prepared with a (Mg²⁺ + Ni²⁺)/Al³⁺ ratio of 2 and a Ni²⁺/Mg²⁺ with ratios of 0.22, 0.47, and 4.05. The structural, textural and redox features of the oxides were investigated by a variety of techniques, including X-ray diffraction, transmission electron microscopy, N₂ physisorption, and temperature-programmed reduction. The acid and base properties were assessed by NH₃ and CO₂ adsorption microcalorimetry, respectively. The acid–base features were also investigated by testing the catalytic behaviors of the oxides for the conversion of 4-methylpentan-2-ol under both mild and stressed conditions. The reactant alcohol can undergo dehydration into 4-methylpent-1-ene, 4-methylpent-2-ene, and skeletal isomers of C₆-alkenes, as well as dehydrogenation to 4-methylpentan-2-one and higher ketones, the product selectivity being governed by the concentration and strength of the acid and base sites. Comparison between the calorimetric and test reaction results is discussed.