Synthesis and characterization of Cr/Cu/Mg mixed oxides obtained from hydrotalcite-type compounds and their application in the dehydrogenation of isoamylic alcohol

Abstract CrCuMg layered double hydroxides (LDH) with hydrotalcite-like structure containing different proportions of Mg 2+ , Cu 2+ and Cr 3+ cations have been prepared. Thermogravimetry and X-ray diffraction data indicate that the transformation of LDH into mixed oxides is effective after calcination at 450 °C. The effect of copper and magnesium for the dehydrogenation reaction of isoamyl alcohol has been examined and high conversions and selectivities to isovaleraldehyde were observed. Experimental data show that the copper is the active specie but the addition of magnesium improves the stability of the catalyst. An exhaustive analysis by XPS allowed us to analyze different copper species in the catalysts. So, Cu 2+ was detected as CuO and as CuCr 2 O 4 spinel-like in calcined samples, while Cu 0 and Cu 2+ were found in the reduced samples, being higher the percentage of the former with the increase of the magnesium content in the sample. Chromium is as Cr 3+ in an octahedral coordination in the precursors as found by diffuse reflectance, and it occupies a similar position to that of aluminium in layered double hydroxides. The LDH are poorly crystalline, but the crystallinity degree increases after calcination, as observed by XRD. Moreover, the specific surface area determined by N 2 adsorption–desorption and the “memory effect” analyzed by DTA, were related to the content of magnesium.