The influence of chemical composition of Mg−Al mixed oxides on their properties and catalytic performance in aldol condensation of furfural and acetone was studied. Pure alumina, Mg−Al layered double hydroxides with a wide range of Mg/Al molar ratios from 0.5 to 15, and pure magnesia were prepared by the same synthesis method, and corresponding oxides were produced by calcination of the as-prepared samples at T = 450 °C. The physicochemical properties of the samples were investigated by XRD, N 2 physisorption, SEM, CO 2 -TPD, and NH 3 -TPD, and their catalytic performance was evaluated in aldol condensation of furfural and acetone. SEM images revealed that the Al content in the samples influenced the size and the morphology of both large agglomerates and plate-like crystals. The CO 2 -TPD measurements proved that the concentration of basic sites and the distribution of their strengths was determined by the Mg/Al molar ratio in the Mg−Al mixed oxides. However, over the whole range of Mg/Al compositions studied here, no clear correlation between the chemical composition and the number and strength of basic sites was found. Nonetheless, the change in the strength and in the density of basic sites affected the catalytic performance of calcined Mg−Al mixed oxides. Additionally, morphology and crystal size also influenced the performance of the catalysts. Finally, the composition of reaction products was affected by acid−base and textural properties of the prepared Mg−Al-mixed oxides.

Basic mixed oxides MgAl, ZnMgAl, and ZnAl were successfully prepared from hydrotalcite precursors synthesized by urea method. Materials with the same molar ratio (M2+/Al3+) = 2 were studied to describe the influence of Mg/Zn ratio on their physicochemical properties. Materials were tested as catalysts of the aldol condensation of furfural with acetone. For samples with similar particle sizes and surface BET areas, the varying catalytic activity was related to the different acidobasic properties. Higher furfural conversion and selectivity to longer carbon chain F2Ac product was observed for samples with higher total amount of basic sites. More specifically, it correlated with the population of Me2+–O2– pairs that represented dominant type of basic sites in all studied catalysts. At the same Al loading, Mg2Al mixed oxide exhibited higher specific surface area, higher total amount of basic sites and higher amount of acid sites than Zn2Al oxide.

The activity of Ni-Al mixed oxides obtained by the thermal pre-treatment of Ni-Al hydrotalcite-like precursors was studied in the ODH of ethane and propane. The activity of the Ni-Al mixed oxide catalysts was studied with respect to (i) the role of Ni content and (ii) the role of temperature during Ni-Al HTs thermal pre-treatment. The structure analysis and the activity of Ni-Al mixed oxides were discussed in three groups; (A) the catalysts pre-treated at 500°C, (B) the catalysts pre-treated at 600°C and (C) the Ni2-Al catalyst with constant Ni content pre-treated at 500-900°C. Ni-Al mixed oxides were active and selective catalysts in the ODH of ethane even at 450°C. On the other hand, the catalysts posses low selectivity to propene. It is supposed that the interaction of NiO with alumina phase plays the critical role in the active and selective catalysts. The Ni-Al mixed oxides were characterized by XRD, H 2 -TPR and diffuse reflectance spectroscopy.

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