The synthesis and application of pillared clays prepared from charge reduced montmorillonite

The synthesis of pillared interlayered clays (PILCs) makes use of the cation exchange capacity (CEC) of clay minerals to prop their structures open with large hydroxy-metal cations.; Homo-ionic Ca-Montmorillonite with a CEC of 83.9 meq/100 g has been partially exchanged with varied amounts of Li+ and heated to 200°C for 24 hours. These have been used to produce Zr and Al PILCs making use of ethanol/water synthesis solutions to overcome the hydrophobic nature of the clay.; For the Zr-PILC system, the d₍₀₀₁₎ spacings determined by x-ray diffraction (XRD) were relatively constant at 19.0–20.1 Å with respect to changing the unpillared CEC. The Zr-PILCs had type I isotherms for argon at 87 K and for benzene, p-xylene and 1,3,5-trimethylbenzene adsorption at 30°C.; Several Al-PILC synthesis procedures were evaluated and all produced materials whose adsorption capacity decreased with decreasing unpillared CEC. This reduction in adsorption capacity with unpillared CEC could be partially overcome by the combined use of ethanol/water pillaring solutions with ethanol/water washing. Previously unreported d₍₀₀₁₎ values in the range of 26.8 to 29.8 Å were observed in Al-PILCs and were often bimodal with the expected values of about 18 Å. These larger d₍₀₀₁₎ values were most prevalent at lower CEC values, if pillaring conditions favored the formation of polymeric species other than the Keggin cation.; A new micropore size distribution model was developed to better understand PILC pore structure. The new model was compared to the Horvath and Kawazoe (1983) model (HK) and the Cheng and Yang (1994) model (CY) using argon adsorption at 87 K on Zr and Al-PILCs. The interlayer spacings determined by XRD for the test PILCs were 9.5 and 8.5 Å for Zr and Al-PILCs respectively. Pore sizes predicted by the new model were 7.5 and 7.3 Å for Zr and Al-PILCs respectively. The new model consistently predicts values that are closer to the interlayer spacing than either the HK or CY models. The new model showed little change in pore size with changes in unpillared CEC for the Zr-PILC system. These results indicate that the limiting dimension in the PILC pore system is the inter-layer spacing and not the inter-pillar spacing. (Abstract shortened by UMI.)...