Porosity and Thermal Stability of Montmorillonite Pillared with Mixed Oxides of Lanthanum, Calcium and Aluminium

Abstract

Montmorillonite intercalated with mixed pillars of lantana and alumina was prepared using a refluxed solution of aluminium chlorohydrate and lanthanum chloride. It is found that there are two main groups of pores in the pillared clays so prepared, one of which is around 8 A, being close to that in alumina pillared clay (Al-PILC) and the other is about 14 A. In contrast to the alumina pillared clays, a significantly larger specific surface area and micropore volume remained in LaAl-PILC after heating at high temperatures (700°C and 800°C). It seems that lanthanum ions react with the clay sheets during heating at high temperatures, resulting in a new porous solid phase which is thermally stable but has poor crystallinity. Calcium cations were introduced into the clays during the pillaring process. The calcium, distributed in the micropores of the product, LaAlCa-PILCs, further enhances the resistance to heating at high temperatures. After heating at 800°C, the BET surface area and micropore volume of a LaAlCa-PILC sample remained at about 138 m2/g and 0.05 cc/g, respectively, with a narrow pore size distribution in the micropore region. The influence of lanthanum and calcium on the pore structure as well as the evolution of pore structure in the PILCs upon heating at high temperatures are discussed in detail.