Catalytic hydrogen transfer from 2-propanol to cyclohexanone over basic Mg-Al oxides

Magnesium-aluminium mixed oxides in mole ratios from 2 to 4 were obtained by thermal decomposition of layered double hydroxides (LDHs) as precursors. The effect of the Mg/Al ratio on the structure and surface properties of the resulting oxides was studied by using various instrumental techniques including X-ray diffraction (XRD), thermogravimetric analyses (TGA), MAS NMR, X-ray photoelectron spectroscopy (XPS) and gas adsorption-desorption, and so was their influence on the catalytic activity of the solids in the hydrogen transfer from 2-propanol to cyclohexanone. The results were compared with those for a pure MgO oxide and the Mg-Al mixed oxide obtained from the LDH with an Mg/Al ratio of 2 was found to provide the best catalytic activity. The influence on catalytic activity of other experimental variables including the pH of the medium used to synthesize the precursor LDHs, the temperature employed to prepare the Mg-Al oxides and the amount of catalyst used was also examined. Catalyst recycling tests were also conducted. Based on the results, a mechanism is proposed for the overall catalytic hydrogen transfer. (C) 2003 Elsevier B.V. All rights reserved.