Al-, Al,Zr-, and Zr-pillared montmorillonites and saponites: Preparation, characterization, and catalytic activity in heptane hydroconversion

Zr- and Zr,Al-pillared smectites have been prepared and characterised by X-ray diffraction and nitrogen sorption measurements. The residual cation exchange capacities and the acid contents have been determined. Hydroconversion of heptane over Pt-impregnated samples was used to evaluate their catalytic properties. The results were compared with those obtained over Al-pillared forms of the same smectites, For the Zr-pillared clays, mixtures of pillared and unpillared fractions were obtained in proportions depending on the preparation conditions. The pillared fractions exhibited poorer thermal resistance than the corresponding Al-pillared forms, Mixed Al,Zr-pillared clays behaved much like Al-pillared clays. The conversion of heptane over the Zr-pillared montmorillonites was substantially enhanced with respect to the Al-pillared analogues, due to the enhanced hydrogenolysis on platinum, Isomerisation activity at the opposite drastically decreased. These changes were less pronounced in the case of the pillared saponites, Zr-pillared saponite with low tetrahedral charge showed an intermediate behaviour. (C) 1999 Academic Press.