SURFACE HETEROGENEITY IN MICROPORES OF PILLARED CLAYS - THE LIMITS OFCLASSICAL PORE-FILLING MECHANISMS

The microporosity of Al-13-intercalated and -pillared synthetic saponi tes with variable layer charge (from 0.8 to 1.5 per unit cell) was stu died by high-resolution quasi-equilibrium adsorption volumetry and low -temperature adsorption microcalorimetry. A strong positive correlatio n was observed between the adsorbed amounts oi: nitrogen and argon and the quantity of intercalated aluminum, suggesting that a simple micro pore-filling is inappropriate to interpret N-2 and Ar adsorption on in tercalated and pillared clays. Adsorption energy distributions were ca lculated using the derivative isotherm summation (DIS) procedure. They reveal that, at 77 K, nitrogen (and argon to a lesser extent) ''titra tes'' the Bronsted acidic sites of the pillars and does not provide di rect information about the liquid microporous volume between pillars. This picture of N-2 and Ar adsorption suggests a critical reexaminatio n of many published data concerning the surface area and porous volume of pillared clays.