Microcalorimetric measurement of the acid properties of pillared clays prepared by competitive cation exchange

The competitive ion exchange of polycations has been used to prepare well ordered Ti, and Fe-pillared clays of high specific surface area from montmorillonite, and from a beidellitic clay either natural or acid treated. The competitor are Al polycations added to the pillaring solutions. The method has been applied to unpurified natural clays, giving PILCs with surface areas of around 250 m2/g after drying at 523 K. The thermal stability of the resulting solids is increased with surface areas as high as 130–220 m2/g after calcination at 773 K. The competitive ion exchange has been also applied to acid treated clays, with surface areas of the PILC reaching 200 m2 g− 1. The acid properties of these PILC, determined by microcalorimetry using NH3 adsorption, are comparable to those of zeolites or supported heteropolyacids, with initial heats of adsorption of 150–160 kJ mol− 1 and site density of around 2 μmol/m2. This acidity overpass that of pillared montmorillonites and saponites prepared by a conventional method. The acid-activated clays pillared by this procedure show a lower acidity than the pillared materials obtained from natural clays.