Acid-base features of ex-hydrotalcites Mg-containing and Mg-free mixed oxides

CuNiAl and MgCuNiAl mixed oxides (Cu2+/Ni2+ = 0.29 and 0.32 mol/mol) were obtained from layered double hydroxide precursors (M 2+/Al3+ = 2 mol/mol) synthesized by pH-controlled co-precipitation. After structural and textural characterization (by X-ray diffraction and N2 physisorption, respectively), the acid and basic features of the mixed oxides were investigated by adsorption microcalorimetry. NH3 and CO2 were used for probing the acid and basic features, respectively. By the use of temperature-programmed technique, the redox features of the oxides were investigated as well. The behaviour of the oxides as catalysts for the conversion of 4-methylpentan-2-ol at 448, 473, and 523 K under atmospheric pressure was studied in a fixed-bed reactor. The dehydration products distribution and the relative extents of the dehydration and dehydrogenation reactions are discussed in terms of the possible occurrence, depending on the lack or presence of Mg in the oxide and the reaction temperature, of either acid-base-governed E1 and E2 mechanisms or Cu-promoted reaction pathways.