Vibrational spectroscopy of H-2, N-2, CO and NO adsorbed on H, Li, Na, K-exchanged ferrierite

The vibrational spectroscopy of H-2, N-2, CO and NO adsorbed on the zeolite ferrierite is described. The spectral modifications induced by the adsorpt ion process on the protonic form are compared with those observed on the al kaline-exchanged forms. Different environments of Bronsted sites and of alk aline counterions in ferrierite are evidenced, which differ in the local el ectric field associated with the cationic species. These different environm ents are associated with the cation locations in the channels and cavities. In particular, ions located in the 10-membered ring channels are more avai lable for the interaction with CO, N-2 and H-2, while ions in the cages for m weaker adducts. On passing from lithium-, to sodium- and to potassium-exc hanged samples; the local fields probed by H-2, N-2 and CO are increasingly dependent upon the distribution of the ions in the framework. In K-ferrier ite the interaction cannot be solely described in terms of 1:1 K+/B (B=N-2, CO) adducts. As far as H-ferrierite is concerned, it is inferred from the observed shift of the v(OH) mode upon interaction with H-2, N-2 and CO that the bridged strong acid groups show an acid strength very similar to that observed for H-ZSM-5, H-mordenite and H-Beta. (C) 2000 Elsevier Science B.V . All rights reserved.