THE EFFECT OF THERMAL TREATMENT ON THE PROPERTIES OF HYDROXY-AL AND HYDROXY-GA

The A1 adsorption maximum for montmorillonite is close to 5.5 mEq A1/g clay, whereas the maximum for Ga is higher. Basal spacings of both Ga- and Al-pillared clays vary between 16.7 and 18.8 ~,. Freeze-drying of pillared products followed by calcination yielded more regular pillared structures. Pillaring montmorillonite increased the BET surface area from 35 m2/g to 350 m2/g mainly by the creation of micropores <20 • in diameter. The Al-pillared clays are thermally stable to ~700 ~ Calcination of pillared montmorillonite liberates protons from the pillar, which diffuse into the clay sheet, lowering the thermal stability. In pillared beidellite, mainly silanol groups are formed by breaking Si-O-AI bonds. No reaction is observed between pillars and montmorillonite upon calcination, whereas in pillared beidellite astructural transformation li ks the pillar to inverted tetrahedra ofthe tetrahedral sheet. The basal spacing of Ga-pillared montmorillonite collapses to 9.5/ ~ at 350 ~ due to the Ga polymer decomposing toGa 3+ cations. The use of clay minerals in catalytic reactions was recognized at the end of the nineteenth century (Von Liebig, 1865). Examples of catalytic reac-tions are simple isomerization and polymerization on palygorskite (Montaland, 1911; Gurwitsch