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 surfactant-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 ion surfactant (Q(+)) by calcination afforded PCH intercalates with basal spacings 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 the supermicropore to small mesopore region similar to 15-23 Angstrom. Temperature-programmed desorption of chemisorbed cyclohexylamine (CHA) indicated the presence of both weak and strong acid sites, corresponding to desorption 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 density (x), indicating that the acidity is correlated with the number of protons balancing the clay layer charge after calcination. The high acidity, structural stability to 750 degrees C, and supermicroporous to small mesoporous pore structure of these intermediates make these PCH materials especially attractive candidates for acid-catalyzed conversions of organic molecules.