Two-phase porous silica: Mesopores inside controlled pore glasses

The structural and textural properties of “Two-Phase Porous Silica” consisting of a mesoporous pore system formed by finely dispersed silica-gel inside the original pores of a macroporous glass framework have been carefully investigated. Nitrogen adsorption at 77 K, Mercury Intrusion, Small Angle X-ray Scattering (SAXS), Temperature-Programmed Desorption (TPD) of ammonia and 27Al MAS NMR spectroscopy were used. Different mesoporous glasses investigated show BET surface areas up to 300 m2/g, a total pore volume of about 0.16 cm3/g and pore sizes of <2–10 nm, depending on the acid leaching conditions of the phase-separated sodium borosilicate initial glass. The texture of the macroporous “frame” glass was characterized after removing the mesoporous finely dispersed silica-gel phase with alkaline solution. Leaching of the phase-separated initial glass with Al(NO3)3 solution and followed by thermal treatment lead to the formation of Bronsted acid sites at the surface of the resulting mesoporous glasses by an incorporation of aluminium in tetrahedral coordination in the silica framework.