Aluminated Derivatives of Porous Clay Heterostructures (PCH) Assembled from Synthetic Saponite Clay: Properties as Supermicroporous to Small Mesoporous Acid Catalysts

Mesostructured aluminosilicate intercalates belonging to the new class of solid acids known as porous clay heterostructures (PCH) have been prepared by the postsynthesis grafting of aluminum into the mesostructured intragallery silica framework of a PCH precursor derived from a synthetic saponite clay. Elemental analyses, powder X-ray diffraction, N 2 adsorption, and 27 Al MAS NMR spectroscopy were used to characterize the reaction products, which we designate Al−SAP/PCH. Depending on the choice of aluminum reagent (AlCl 3 or NaAlO 2 ), the Al−SAP/PCH derivatives exhibited basal spacings of 32−34.8 Å, BET surface areas of 623−906 m 2 /g, pore volumes of 0.32−0.45 cm 3 /g, and pore sizes in the large micropore to small mesopore range (14−25 Å). The aluminum content was strongly correlated with the Si/Al stoichiometry of the postsynthesis reaction mixture. Nearly all of the grafted aluminum was incorporated into tetrahedral sites in the intragallery silica framework. In comparison to the initial silica-intercalated SAP/PCH precursor, little or no change in textural porosity was observed when the alumination reaction was carried out under acidic conditions using aqueous AlCl 3 as the aluminum source. Also, only small decreases in surface area and pore volume were noted when NaAlO 2 was used as the alumination reagent under basic conditions. Both alumination reagents afforded protonated Al−SAP/PCH derivatives with increased acidity in comparison to the initial silica-intercalated SAP/PCH precursor, as verified by temperature-programmed desorption of cyclohexylamine and catalytic reactivity for cumene cracking.