Preparation and Properties of Sodalite-Type Aluminophosphates Containing Silicon, Cobalt and Zinc

Abstract

The SAPO, MeAPO and MeSAPO microporous materials (Me=Co²⁺ and/or 2n²⁺) having a sodalite structure have been obtained hydrothermally at 200°C in the presence of tetramethylammonium ion as the template. The SAPO and MeSAPO products prepared at lower template concentrations are formed through a partial replacement of both aluminium and phosphorus by silicon in the parent aluminophosphate lattice; at higher pH only phosphorus is replaced. While the Me²⁺ ions are in all cases constituents of the framework, most zinc-containing materials have a fraction of the Zn²⁺ ions located in the cavities. T.g.a . shows that complete removal of the trapped organic component can not be easily accomplished. This can be explained by the small size of the openings in the sodalite cages. Powder diffraction analysis shows that replacement of aluminium by silicon, cobalt and zinc, and phosphorus by silicon leads to an expansion of the parent aluminophosphate unit cell. Kinetic studies suggest that crystallization of the silicon-containing products is preceded by an induction period of about 2 h, the nucleation taking place both in the liquid and solid phase.