Novel acidic solids from high charge Na-micas by mild hydrothermal treatment

A new meso-porous structure with a significant increment in the acidity and surface area has been developed from a novel family of swelling brittle micas - Na-n-Mica (n = 2, 3 and 4), where n is the layer charge per unit cell - for the first time. The uncommon high charge micas with up to four interlayer cations per unit cell have been synthesized following the "NaCl melt method", and treated with an aluminium aqueous solution in a Teflon vessel closed in a stainless steel reactor at 150 °C for 48 h. The diffusion of aluminium hydroxide complexes into the bidimensional galleries of the silicate has been successfully achieved in the three samples avoiding any pre-swelling step, and confirmed by XRD. After hydrothermal treatment, inherent acidic sites located in the tetrahedral layer of those swelling micas become accessible by the formation of a partially delaminated-intercalated structure, creating a new interesting family of highly acidic materials. Finally, thermal stability of the acidic centres, and textural properties of the synthesized samples after calcination have been also tested.