Modified layered silicates as acid catalysts

• Main Author: Bovey, J.
• Published: University of Cambridge 1996
• Subjects: 541.39
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596810

Three montmorillonites were modified by ion exchange, acid activation and pillaring. The acid activated clays were further pillared with Al, Ti, Zr or Cr polycations to produce pillared acid activated clays. Characterisation techniques included powder X-ray diffraction, FTIR spectroscopy, elemental analysis, N<SUB>2</SUB> porosimetry and thermogravimetry. Characterisation revealed that the properties of the acid activated products were dependent upon the nature of the starting material and the conditions of activation. In turn, the properties of the pillared acid activated derivatives depended upon the particular and activated host and were generally intermediate between those of pillared raw clays and acid activated clays. In general, they possessed higher surface areas, pore volumes and acidities, wider pore size distributions and larger average pore diameters than their pillared raw counterparts. Variation of the pillaring cation revealed that the properties of the pillared acid activated materials depended on the pillar identity. Total surface areas and pore volumes of the Zr pillared materials were higher than those of the A1 pillared and Ti pillared counterparts. In general, Al pillared materials were the most microporous and Ti pillared materials were the most mesoporous. Three different methods reported in the literature were used to produce Ti pillared clays. Two of these methods led to products which did not appear to be pillared and which contained high amounts of precipitated anatase. A third method was successfully employed to produce Ti pillared acid activated clays and Ti pillared raw clays. The thermal stabilities of the products critically depended upon the identity of the host clay. Materials of maximal surface areas with large pore volumes were only formed upon calcination at 400 - 500<SUP>o</SUP>C. All the modifications of the original clays resulted in improved catalytic activity for a variety of acid catalysed reactions. In general, Al, Zr and Cr pillared acid activated clays were more active catalysts than their pillared raw counterparts. Ti pillared acid activated clays were, however, slightly less active than Ti pillared raw clays. The activities of the Ti pillared materials were comparable to those of the acid activated clays. In the one case examined, an overall order of activity existed which dependent on the identity of the pillaring cation such that Ti > Zr > Al ≥ Cr.