Novel rare earth exchanged silicoaluminophosphate catalysts (small pore, 0.43 nm) of chabazite type have been prepared. The rare earth elements europium (Eu), gadolinium (Gd) and terbium (Tb) were used for preparing the cation exchanged chabazite type SAPO-18 catalysts. Routine and sophisticated instrumental techniques were used for the material characterisation, The FT-IR technique was used to study the in situ interaction of NO on the rare earth exchanged SAPO-18 catalysts. The adsorption of NO on the Eu-, Gd-, Tb-exchanged SAPO-18 samples led to the formation of nitrous oxide, mono- and dinitrosyl complexes of Eu, Gd and Tb, nitrogen dioxide and nitrate species. (C) 2000 Elsevier Science B.V. All rights reserved.