Nature of nitric oxide and nitrogen dioxide adsorbed on chromium and nickel exchanged zeolites. Electron spin resonance and infra-red study

Abstract

Cr³⁺ exchanged zeolites can be either oxidized to Cr⁵⁺ by oxygen or reduced by H₂ or CO to a lower valence state mainly Cr²⁺. E.s.r. measurements showed the formation of a 3d⁵NO⁺ complex upon adsorption of NO on reduced chromium samples. It was suggested that this complex has a Cr⁺NO⁺ structure and i.r. spectroscopy provided unambiguous evidence of the formation of the nitrosyl complex. Under certain conditions a diamagnetic complex [graphic omitted] was also formed. Adsorption of NO₂ gave rise to the 3d⁵ complex Cr⁺NO⁺₂. Similarly NO and NO₂ adsorb on Ni²⁺ exchanged zeolites to form 3d⁹ complexes. Simultaneously at high pressures NO adsorbs irreversibly on Na⁺ ions of either the exchanged Y zeolites or even the unexchanged NaY. NO adsorption could also be used as a rough but easy means to locate the exchanged cations and to show cation migration from hidden sites towards accessible ones. The behaviour of the zeolite framework as a polar solvent and its probable role in the stabilization phenomenon of some cations in rather unusual valence states is emphasized.