Comments on “Enhanced Thermal Stability of Al-Pillared Smectites Modified with Ce And La” By J.L. Valverde, P. Cañizares, M.R. Sun Kou, and C.B. Molina

Abstract

Valverde et al. (2000) recently reported on the preparation and characterization of Al-pillared smectites modified with Ce and La. Pillaring of clays with Al polyoxocations (Keggin type Al13) and a large variety of other complexing cations has been reported many times since the seventies. McCauley (1988) described in a patent the preparation of thermally stable pillared clays with large basal spacings of ~28 A , followed by publications by Sterte (1991a, 1991b) and Booij and coworkers (Booij et al., 1996a, 1996b). These authors used hydrothermally treated or refluxed solutions containing the Al polyoxocation and the rare earth elements in the form of their chloride salts. The presence of cerium or lanthanum seems to promote polymerization of the Al polyoxocation. Until now however, nobody has been able to assess the structure of the newly formed pillaring molecules. Although the inter-layer spacing is about twice that of the normal Al-pillared clay, chemical analyses indicate smaller amounts of Ce and La than expected from polymerization of the Al polymer alone. Several other studies on the combination of Al pillars with Ce or La resulted in the formation of pillared clays with basal spacings characteristic of Al-pillared clays. However, catalytic activity is enhanced owing to Ce or La ( e.g., Gonzalez et al., 1992; Mendioroz et al., 1993; Trillo et al., 1993). Unfortunately, Valverde and coworkers (Valverde et al., 2000) missed most …