Characterization and application of layered double metal hydroxides

The thermal and spectroscopic properties of fatty acid-exchanged lithium aluminum layered double metal hydroxides (LiAl-LDHs) are examined. In an anaerobic environment, the layered structures expand with an increase in temperature. A bilayered arrangement of the fatty acid molecules is formed at temperatures above 100{dollar}spcirc{dollar}C. The layered structures are stable up to temperatures of 250{dollar}spcirc{dollar}C. Differential thermal analysis indicates that there is a partial dehydroxylation of the metal layer at 250{dollar}spcirc{dollar}C. This results in a material of considerably high surface area and the direct association of the exchanged fatty acids with the lithium atoms in the framework. The fatty acid chains after heat treatment assume a disordered state which is retained upon cooling the sample. The high porosity and the hydrophobicity make these materials candidates for stationary phases in gas chromatography. The mechanisms of retention for various sets of molecules are examined using several different fatty acid exchanged LDHs.; Fatty acid exchanged LDHs, along with organic-clay, are also used as secondary supports for methanol catalysis. The layered materials are pillared with vanadium and titanium by using the hydrophobic interlayered environment to adsorb vanadium and titanium alkoxides. The calcination of these samples results in microporous materials with high surface areas. Spectroscopic evidence indicates that the mixed pillars are similar in structure to monolayer supported vanadium catalysts such as V{dollar}sb2{dollar}O{dollar}sb5{dollar}/TiO{dollar}sb2{dollar}. The layered materials are very active methanol catalysts and are selective for the oxidation of methanol to formaldehyde at temperatures up to 270{dollar}spcirc{dollar}C.