The acid-base and red-ox properties of amorphous magnesium and zinc molybdates obtained through calcination at 400 degrees C of Mg2Al- and Zn2Al-heptamolybdate layered double hydroxides, which had been prepared by anionic exchange from the corresponding nitrate -hydrotalcite precursors, have been studied. Lewis-type acid and basic sites have been detected in both systems, in addition to Bronsted-type acid sites in magnesium molybdate; however, as studied by FT-IR spectroscopy, none of them is strong enough to yield propene through isopropanol decomposition. The higher reducibility of Mo6+ cations in zinc-containing samples than the magnesium containing ones makes them more selective for acetone production. Moreover, a small amount of products formed on basic sites through acetone aldol reaction have been identified at high reaction temperatures. (c) 2006 Elsevier B.V. All rights reserved.