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