PREPARATION, STRUCTURAL CHARACTERISTICS AND CATALYTIC PROPERTIES OF LARGE-PORE RARE-EARTH ELEMENT (CE,LA) AL-PILLARED SMECTITES/

Ce/Al- and La/Al-pillared smectites were prepared by cation exchange o f bentonite, saponite and laponite with hydrothermally treated (130-16 0 degrees C for 16-136 h) solutions containing mixtures of aluminumchl orohydrate (ACH) and Ce3+-/and La3+ salts. After calcination at 500 de grees C, the pillared products are characterized by basal spacings bet ween 24.8 and 25.7 Angstrom and surface areas of approximately 430 m(2 ) g(-1). The products are hydrothermally stable at 500 degrees C after 2 h in steam. The large basal spacings are due to the formation of a large Ce/La-bearing Al-polyoxocation, whose formation is favored by in itially high Al concentrations greater than or equal to 3.7 M and an O H/Al molar ratio of approximately 2.5. The Ce/Al or La/Al molar ratios can be as low as 1/30. Al-27 nuclear magnetic resonance (NMR) spectro scopy has shown that the polyoxocation has a higher Al-tetrahedral/Al- octahedral ratio than the Keggin structure Al-13, which may partly exp lain the higher stability compared to normal Al-pillared clays. Hydroc onversion of n-heptane indicated that the activity of the Pt-loaded pi llared products is higher than that of a conventional Pt-loaded amorph ous silica-alumina catalyst. Selectivity is strongly dependent on the type of starting clay and its acidity. In industrial hydrocracking of normal feedstock, a Ni/W-loaded Ce/Al-pillared bentonite catalyst show ed rapid deactivation due to coke-formation reducing the surface area and the pore volume. Additionally, coke-formation is facilitated by th e relatively high iron content of the pillared bentonite (3.43 wt% Fe2 O3).