Acidic porous clay heterostructures (PCN): Intragallery assembly of mesoporous silica in synthetic saponite clays

Mesostructured intercalates belonging to the class of solid acids known as porous clay heterostructures (PCH) have been prepared through the surfactan t-directed assembly of mesoporous silica within the galleries of synthetic saponite clays with targeted layer charge densities in the range x = 1.2-1. 7 e(-) units per Q(x)(+)[Mg-6](Si8-xAlx)O-20(OH)(4) unit cell. The removal of the intragallery mixture of neutral alkylamine and quaternary ammonium i on surfactant (Q(+)) by calcination afforded PCH intercalates with basal sp acings of 33-35 Angstrom, BET specific surface areas of 800-920 m(2) g(-1), and pore volumes of 0.38-0.44 cm g(-1). The framework pore sizes were in t he supermicropore to small mesopore region similar to 15-23 Angstrom. Tempe rature-programmed desorption of chemisorbed cyclohexylamine (CHA) indicated the presence of both weak and strong acid sites, corresponding to desorpti on temperatures near 220 and 410 degrees C, respectively. The total acidity (0.64-0.77 mmol CHA g(-1)) increased with the saponite layer charge densit y (x), indicating that the acidity is correlated with the number of protons balancing the clay layer charge after calcination. The high acidity, struc tural stability to 750 degrees C, and supermicroporous to small mesoporous pore structure of these intermediates make these PCH materials especially a ttractive candidates for acid-catalyzed conversions of organic molecules.