Characterization of AlCu and AlCuMg mixed oxides and their catalytic activity in dehydrogenation of 2-octanol

Hydrotalcite (HT) type materials with different Cu:Mg:Al ratios were prepared. The samples were calcined at 450 °C and when the layered structure was destroyed mixed oxides were formed. Such oxides were reduced under a flow of hydrogen gas at 300 °C and their catalytic activity in dehydrogenation of 2-octanol was studied. High conversion and selectivity towards 2-octanone was observed. The samples without copper showed low conversion, but it increased with the copper content. The characterization of both precursors and reduced catalysts was carried out by XRD, XPS and diffuse reflectance. In the calcined samples, the XPS analysis detected Cu2+ in a CuAl2O4 spinel-like environment as well as CuO, while the reduced samples contained Cu0 and copper ions, such as Cu2+ and Cu+. Diffuse reflectance showed that the copper was present in two forms, the perfect and distorted octahedra. In the AlCuMg system, the copper was present in a cluster-like or bulk-like species, excepting the samples having a copper excess, where a spinel-like species was detected. By XRD, a greater structural ordering was observed in the samples containing a ratio Cu2+/Mg2+ ≤ 1 (Cu < 50% keeping in mind only cations M2+) and in those having a ratio (M3+/M3+ + M2+) approximately equal to 0.25; in this case other species were not detected.