Nitrosylic complexes in Ag(I)-ZSM-5: a comparison with Cu(I)-ZSM-5

Starting from (NH4)(+)-ZSM-5, we have prepared Ag(I)-ZSM-5 and Cu(I)-ZSM-5. In both cases a nearly total cation exchange has been achieved. The local environment of AE(I) and Cu(I) cations, as determined by an EXAFS study, is very similar in both cases: Cu(I) is surrounded by 2.5+/-0.3 oxygen atoms at 2.00+/-0.02 Angstrom and Ag(I) is surrounded by 2.5+/-0.5 oxygen atoms at 2.30+/-0.03 A. Notwithstanding the same electronic configuration of the two cations (d(10)), nitrosylic complexes formed in the two systems exhibit quite consistent differences. At liquid-nitrogen temperature, in Cu(I)-ZSM-5, IR spectroscopy reveals the stepwise formation of [Cu(NO)](+) and [Cu(NO)(2)](+) complexes, whereas only mononitrosylic [Ag(NO)](+) has been observed in Ag(I)-ZSM-5; moreover, the stability of cuprous nitrosylic adducts upon decreasing the NO equilibrium pressure and/or increasing the sample temperature has been observed to be much greater than that of corresponding silver nitrosylic adducts. Our results indicate that, in contrast to Cu(I), the interaction between NO and Ag(I) cations hosted in zeolitic systems is mainly of an electrostatic nature. (C) 1999 Elsevier Science B.V. All rights reserved.