Effect of calcination on location and valency of lanthanum ions in zeolite Y

Abstract

The effect of calcination temperatures from 40° to 500°C on the location and effective valency of lanthanum ions in zeolite Y (LaNaY) has been studied. At 60°C lanthanum ions, initially only sited in the supercages, started to diffuse through the six-membered ring separating the supercages from the small cavities (i.e. sodalite cages and hexagonal prisms). La(H 2O) x 3+ species, rather than bare lanthanum ions, are believed to pass through the six-membered ring. The amount of lanthanum locked in the small cages was found to be proportional to the degree of dehydration. The sodium cation exchange capacity (Na CEC) decreased with the increasing degree of irreversible lanthanum migration. The apparent charge on the lanthanum ion was reduced from 3+ at 100°C to 2+ at temperatures > 200°C. This charge reduction was accompanied by the formation of hydroxyl groups and protons from water molecules on the hydrated lanthanum ions. Dealumination was observed during the calcination stage. Results indicate that four protons are required to remove one such aluminium from the framework.