Large pore REE/Al pillared bentonites: Preparation, structural aspects and catalytic properties

Ce/Al and La/Al pillared bentonites were prepared by cation-exchange of different bentonites with hydrothermally treated (130-160°C for 16-136 h) solutions containing mixtures of aluminiumchlorohydrate (ACH) and REE (Ce and La)-salts. After calcination at 500°C the pillared clays are characterised by basal spacings of 24.8-25.7 A, and have BET surface areas of approximately 430 m²/g. The pillared products are hydrothermally stable to at least 500°C. The large basal spacings and surface areas are due to the formation of large REE/Al containing polyoxycations. The formation of this cation is favoured by high initial Al concentrations (≥ 3.7 M) and an OH/Al molar ratio of approximately 2.5. Ce/Al or La/Al ratios can be as low as 1/30. Hydroconversion of n-heptane indicated that the activity of these materials is higher than that of a conventional Pt loaded amorphous silica alumina (ASA) reference catalyst. The selectivity is strongly dependant on the type of starting clay. In industrial hydrocracking of normal feedstock, a Ni/W loaded REE/Al pillared clay catalyst showed slightly higher initial activity than the ASA reference catalyst. However, the pillared clay catalyst showed rapid deactivation due to coke-formation, which reduced the surface area and pore volume. Additionally coke formation may be facilitated by the relatively high iron content of the pillared bentonite (3.43 wt%).