Synthesis and characterization of Cr/Cu/Mg mixed oxides obtained

M CRIVELLO; C PEREZ; J FERNANDEZ; G EIMER; E HERRERO; S CASUSCELLI; E RODRIGUEZ CASTELLON

APPLIED CATALYSIS A-GENERAL

Elsevier Science B.V., Netherlands. Editors: Prof. H.H. Kung, Evanston, USA. Prof. K. Segawa, Tokyo, Japan. Prof. J.C. Vedrine, Liverpool, UK.

Año: 2007 vol. 317 p. 11 - 19

0926-860X

CrCuMg layered double hydroxides (LDH) with hydrotalcite-like structure containing different proportions of Mg2+, Cu2+ and Cr3+ 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 8C. 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 ofmagnesium improves the stability of the catalyst. An exhaustive analysis by XPS allowed us to analyze different copper species in the catalysts. So, Cu2+ was detected as CuO and as CuCr2O4 spinel-like in calcined samples, while Cu0 and Cu2+ 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 Cr3+ 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 N2 adsorption?desorption and the ??memory effect?? analyzed by DTA, were related to the content of magnesium.