Pillared Clays: Chemistry and Prospects

Pillaring of smectites with Al consists of three processes: (i) ion exchange of the Al₁₃7+ Keggin ion; (ii) hydrolysis of the Keggin ion upon contact with the clay surface; (iii) precipitation of the Keggin ion on the clay particles. Conditions can be chosen to limit the pillaring to the first two processes. Smectites with Al in the tetrahedral layer are the preferred materials for pillaring. Thus, pillared saponite is an excellent acid catalyst. In other catalytic applications and in selective adsorption pillared clays perform well, but cannot yet compete successfully with the available microporous and mesoporous materials.