THE A1 PILLARING OF CLAYS .1. PILLARING WITH DILUTE AND CONCENTRATED A1 SOLUTIONS

Saponite, hectorite, and laponite have been pillared with cationic Al clusters, and special attention has been given to the solution chemist ry of Al. Pillared saponite is obtained after exchange with refluxed A l solutions; while for hectorite, Al solutions treated with ammonium a cetate give a pillared product with 1.8-1.9 nm spacing and thermal sta bility up to 873 K. In both types of solutions, the Keggin ion Al clus ter is a minority species or totally absent. The typical 1.8-1.9 nm sp acing is only obtained after washing. The quality of the pillared mate rial can be judged From its thermal stability, its surface area, and t he width of the d001 line before and after pillaring. The width should not exceed 0.3 nm before calcination and 0.5 nm after calcination. Th e latter criterion reflects the importance of the crystallinity of the parent clay for successful pillaring. Pillaring in concentrated condi tions occurs by a combination of ion exchange and precipitation of Al and gives materials that exhibit poor thermal stability.