Probing the surface acidity of lithium aluminium and magnesium aluminium layered double hydroxides

Abstract

The surface acidity of a range of lithium aluminium layered double hydroxides intercalated with carbonate, chloride, nitrate and decavanadate anions has been measured using Hammett indicators. In addition, the adsorption of pyridine and isopropanol has been monitored using infrared spectroscopy. The properties of the materials have been compared to their magnesium aluminium analogues. Surface measurements are compared with the observed catalytic activity for acetaldehyde self-condensation 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 elevated temperatures which yielded the most active catalysts (ca. 450C). The order of acidity of the materials varied with the nature of the anion such that: carbonatenitratechloridedecavanadate. Thus it was concluded that the nature of the interlayer anion had a large effect on the acidity of the materials, although the acidity was largely unaffected by the identity of the host matrix itself.