Layered double hydroxides and their pillared derivatives -: materials for solid base catalysis;: synthesis and characterization

Mg-Al and Zn-Al L(ayered) D(ouble) H(ydroxide)s have been prepared and characterized. Thermal and dehydration/rehydration behaviour was studied by thermoanalytical methods (TG, DTG, DTA) and Al-27 M(agic) A(ngle) S(pinning) NMR spectroscopy, X-ray diffractometry (XRD) and S(canning) E(lectron) M(icroscopy). Acid-base properties of the calcined samples were investigated by T(emperature) P(rogrammed) D(esorption) of preadsorbed CO2 and the double-bond isomerization reaction of 1-butene. Heat treatment destroyed the layered structure, which could be only partially reconstituted by rehydration. On calcination mixed oxide with the predominance of basic sites were formed. Pillaring of the LDHs with organic (terephtalate, dodecyl sulphate) as well as inorganic (oxometallate, ferrocyanide) anions were also performed. The materials were characterized by infrared (IR) spectroscopy, XRD and BET measurements. Heat stabilities of the pillared substances were investigated too. pillaring by various methods proved to be successful, however, decreased heat resistance was found in the intercalated materials relative to the host LDHs. (C) 1999 Elsevier Science B.V. All rights reserved.