PROBING THE SURFACE-ACIDITY OF LITHIUM ALUMINUM AND MAGNESIUM ALUMINUM LAYERED DOUBLE HYDROXIDES

The surface acidity of a range of lithium aluminium layered double hyd roxides intercalated with carbonate, chloride, nitrate and decavanadat e anions has been measured using Hammett indicators. In addition, the adsorption of pyridine and isopropanol has been monitored using infrar ed spectroscopy. The properties of the materials have been compared to their magnesium aluminium analogues. Surface measurements are compare d with the observed catalytic activity for acetaldehyde self-condensat ion and 2-methylbut-3-yn-2-ol conversion. The MgAl matrix was found to be more stable than the LiAl matrix following calcination at the elev ated temperatures which yielded the most active catalysts (ca. 450 deg rees C). The order of acidity of the materials varied with the nature of the anion such that: carbonate < nitrate < chloride < decavanadate. Thus it was concluded that the nature of the interlayer anion had a l arge effect on the acidity of the materials, although the acidity was largely unaffected by the identity of the host matrix itself.