Acido-basic and catalytic properties of transition-metal containing Mg–Al hydrotalcites and their corresponding mixed oxides

Acido-basic MMgAlO mixed oxide catalysts (M = Mn, Fe, Co, Ni, Cu and Zn) were obtained by thermal decomposition of the corresponding layered double hydroxide (LDH) precursors. They were characterized by XRD, EDX, nitrogen adsorption, TG-DTG, NH3-TPD and CO2-TPD experiments. The cyanoethylation of methanol was used as a model reaction to evaluate the basicity of the LDHs and the corresponding mixed oxides. Mixed oxides were much more active than their LDH precursors, while both were quite selective for β-metoxypropionitrile. A straight correlation between the number of basic sites of the mixed oxides determined by CO2-TPD and their catalytic activity was evidenced. However, the equilibrium between the acid and basic sites is a key factor determining the catalytic activity.